Systematic Review: The Persistent Association Between Infant Antibiotic Exposure and Childhood Asthma After Accounting for Confounding by Indication and Reverse Causation

Systematic Review: The Persistent Association Between Infant Antibiotic Exposure and Childhood Asthma After Accounting for Confounding by Indication and Reverse Causation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Systematic Review Systematic Review: The Persistent Association Between Infant Antibiotic Exposure and Childhood Asthma After Accounting for Confounding by Indication and Reverse Causation Safana Abdullah Algutaini, Nabil Aljuma'ai This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8355065/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background Early-life antibiotic exposure has been repeatedly associated with an increased risk of childhood asthma. However, this association is vulnerable to substantial methodological bias, particularly confounding by indication (CbI) and reverse causation (RC). This systematic review evaluates whether the association persists in studies employing advanced epidemiologic methods designed to mitigate these biases. Methods A systematic search of PubMed, Embase, Web of Science, and the Cochrane Library was conducted from January 2010 through December 11, 2025 . Eligible publications included (1) primary observational studies (cohort or case-control designs) evaluating antibiotic exposure during infancy (0–24 months) and physician-diagnosed asthma at ≥ 4 years, and/or (2) systematic reviews/meta-analyses that explicitly evaluated or stratified results by approaches addressing CbI and/or RC (e.g., adjustment for respiratory tract infections, exclusion of early wheezing, or comparable bias-mitigation strategies). Study selection followed PRISMA 2020 guidelines. Methodological quality was assessed using the Newcastle–Ottawa Scale for primary studies; systematic reviews were assessed narratively for relevance to the review objective. Results Four eligible studies were included. Crude observational estimates reported in meta-analytic syntheses demonstrated a strong association (pooled OR ≈ 1.37). In analyses explicitly addressing CbI and RC, estimates attenuated but remained statistically significant (pooled OR 1.19; 95% CI, 1.11–1.28). In contrast, a nationwide sibling-matched cohort study eliminated the association for fetal exposures and non-respiratory indications, suggesting substantial familial confounding. A persistent association remained only for antibiotics prescribed for respiratory infections (sibling-matched HR 2.36), consistent with residual confounding by illness severity. Conclusion The association between infant antibiotic exposure and childhood asthma is largely explained by shared familial factors and residual confounding related to respiratory illness severity rather than a direct causal effect of antibiotics. While biological plausibility via gut microbiome disruption remains, current epidemiologic evidence does not strongly support causality. Further studies using advanced causal inference methods are warranted. antibiotics asthma infancy confounding by indication reverse causation sibling analysis epidemiology Figures Figure 1 1. Introduction Childhood asthma is one of the most prevalent chronic pediatric conditions worldwide and arises from a complex interplay between genetic susceptibility and environmental exposures. Observational studies have repeatedly reported positive associations between antibiotic exposure in infancy and subsequent childhood asthma, prompting hypotheses that microbiome disruption during immune development may contribute to asthma pathogenesis. However, causal interpretation is complicated by two major biases: confounding by indication , where antibiotics are prescribed for respiratory tract infections (RTIs) that independently increase asthma risk, and reverse causation , where early asthma symptoms are misdiagnosed as infection and treated with antibiotics. This systematic review focuses on evidence that explicitly addresses these biases using advanced epidemiologic strategies, including sibling-matched designs and analyses adjusting for RTIs or excluding early wheezing. 2. Methods 2.1 Search Strategy A systematic literature search was conducted in PubMed, Embase, Web of Science, and the Cochrane Library for studies published between January 2010 and December 11, 2025 . Search terms included combinations of antibiotics , infant , early life , childhood asthma , confounding by indication , reverse causation , and sibling analysis . Reference lists of eligible studies and relevant reviews were manually screened. 2.2 Eligibility Criteria Eligible publications included: Primary observational studies (cohort or case-control) evaluating antibiotic exposure during infancy (0–24 months) and reporting physician-diagnosed asthma at ≥ 4 years with explicit strategies to mitigate CbI and/or RC , including sibling-matched designs, exclusion of early wheezing, or explicit adjustment for respiratory tract infections; and/or Systematic reviews/meta-analyses that explicitly evaluated the impact of CbI and/or RC mitigation (e.g., subgroup analyses restricted to studies addressing these biases). Publications were excluded if they: (1) assessed asthma prior to age 4 as the primary outcome, (2) did not distinguish timing of antibiotic exposure in infancy, or (3) did not evaluate or stratify findings by approaches addressing CbI/RC. 2.3 Study Selection Two reviewers screened titles/abstracts and full texts. Disagreements were resolved by consensus. Study selection is summarized in the PRISMA 2020 flow diagram (Fig. 1). 2.4 Data Extraction Extracted data included study design, population characteristics, exposure definition, asthma outcome definition, bias-mitigation methods (CbI/RC), and effect estimates (OR/HR) with confidence intervals. 2.5 Quality Assessment Primary observational studies were assessed using the Newcastle–Ottawa Scale. Systematic reviews/meta-analyses were assessed narratively for alignment with the objective and transparency of subgroup/sensitivity analyses addressing CbI/RC. 2.6 Data Synthesis Due to heterogeneity in study designs and analytical strategies, a narrative synthesis was performed, emphasizing comparisons between crude estimates, bias-adjusted meta-analytic estimates, and sibling-controlled analyses. 3. Results 3.1 Study Characteristics Four eligible publications were included in the final synthesis (Table 1 ). Study selection is summarized in the PRISMA 2020 flow diagram (Fig. 1). 3.2 Evidence from Meta-Analyses Addressing CbI and RC Zhang et al. (2021) reported a pooled crude association (OR 1.37; 95% CI, 1.29–1.45) and demonstrated attenuation in analyses of studies that adjusted for CbI and RC (OR 1.19; 95% CI, 1.11–1.28). Lu et al. (2023) similarly reported an attenuated but persistent association after bias adjustment in included studies. 3.3 Evidence from Sibling-Matched Designs Örtqvist et al. (2014) employed a nationwide sibling-matched cohort design. Associations observed in conventional cohort analyses for fetal exposure and non-respiratory indications were eliminated in sibling comparisons (fetal exposure HR ≈ 0.99; non-respiratory indication HR ≈ 0.85). In contrast, antibiotic exposure for respiratory indications remained associated with asthma in sibling analyses (HR 2.36), consistent with residual confounding by severity or type of underlying respiratory illness. 4. Discussion This review indicates that much of the reported association between infant antibiotic exposure and childhood asthma is likely explained by confounding and reverse causation. Meta-analytic estimates attenuate when studies account for these biases, suggesting that crude associations overestimate any true effect. The strongest evidence comes from sibling-matched analyses demonstrating that familial confounding explains associations for fetal exposure and non-respiratory indications. The remaining association observed for respiratory-indication antibiotics likely reflects residual confounding by infection severity rather than a direct antibiotic effect. Although antibiotic-driven microbiome disruption remains biologically plausible, current epidemiologic evidence does not strongly support a causal relationship. Future research should prioritize designs and analyses that more directly address unmeasured confounding and infection severity, including causal inference frameworks and longitudinal microbiome studies. Contextual note (not included in synthesis) Okubo et al. (2021) evaluated antibiotic treatment during hospitalization for asthma exacerbation and was not included because it did not assess infant exposure (0–24 months) leading to incident asthma at ≥ 4 years. 5. Limitations This review is limited by heterogeneity across included studies in exposure ascertainment, asthma diagnostic criteria, and the operationalization of bias-mitigation strategies. Publication bias is possible. Sibling-matched designs cannot account for non-shared factors such as individual-level differences in infection severity. Additionally, relatively few studies apply advanced causal inference methods, limiting definitive causal conclusions. 6. Conclusion The association between infant antibiotic exposure and childhood asthma is largely attributable to shared familial factors and residual confounding by respiratory illness severity. Evidence for a direct causal effect is limited. Rigorous causal inference studies are needed to clarify remaining uncertainties and to test microbiome-mediated mechanisms. References Zhang Z, Wang J, Wang H, Li Y, Jia Y, Yi M, Chen O. Association of infant antibiotic exposure and risk of childhood asthma: a meta-analysis. World Allergy Organ J. 2021;14(11):100607. https://pmc.ncbi.nlm.nih.gov/articles/PMC8661061/ Örtqvist AK, Lundholm C, Kieler H, Ludvigsson JF, Fall T, Ye W, Almqvist C. Antibiotics in fetal and early life and subsequent childhood asthma: nationwide population based study with sibling analysis. BMJ. 2014;349:g6979. https://www.bmj.com/content/349/bmj.g6979 Penders J, Vink C, Driessen GJ, London N, Thijs C, Stobberingh EE. Infant antibiotic use and wheeze and asthma risk: a systematic review and meta-analysis. Eur Respir J. 2011;38(2):295–302. https://publications.ersnet.org/content/erj/38/2/295 Lu Y, Li Z, Zhang Y. Early-life antibiotic exposure and childhood asthma: a systematic review and meta-analysis. Pediatr Pulmonol. 2023;58(3):1010–1020. https://pmc.ncbi.nlm.nih.gov/articles/PMC9952656/ Tables Table 1. Characteristics of Included Studies Study Country Design Sample Size Exposure Definition Asthma Outcome Definition CbI/RC Mitigation Approach Key Findings / Notes Zhang et al., 2021 Multi-country Meta-analysis >1,000,000 (combined) Antibiotic exposure in infancy (varied across included studies) Asthma assessed ≥4 years (study-dependent) Subgroup analyses of studies addressing CbI/RC Crude OR 1.37; bias-mitigated subgroup OR 1.19. Örtqvist et al., 2014 Sweden Population-based cohort + sibling-matched 1.8 million Fetal and early-life antibiotics; indication-stratified Childhood asthma Sibling matching; infection-related controls Association eliminated for fetal/non-respiratory; persistent for respiratory indications (HR 2.36). Penders et al., 2011 Netherlands Systematic review/meta-analysis 22 studies Infant antibiotic exposure Wheeze/asthma (varied); asthma commonly ≥5 yrs Infection adjustment in included studies Provides contextual pooled evidence; susceptibility to residual confounding acknowledged. Lu et al., 2023 China Systematic review/meta-analysis 34 studies Early-life antibiotic exposure Childhood asthma (commonly ≥5 yrs) Adjusted analyses for RTIs/early wheeze Attenuated but persistent association after adjustment. Note: Table includes both primary observational studies and systematic reviews/meta-analyses that explicitly addressed confounding by indication and/or reverse causation. Additional Declarations The authors declare no competing interests. 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14:13:57","extension":"html","order_by":14,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":32721,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8355065/v1/1dc454e5b617f0878675a1ab.html"},{"id":98323218,"identity":"e1836a3d-2653-4adb-b64a-1664963397fc","added_by":"auto","created_at":"2025-12-16 14:13:57","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":50560,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePRISMA 2020 Flow Diagram\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFlow diagram summarizing identification, screening, eligibility assessment, and inclusion of studies in the systematic review. A total of 15,420 records were identified through database searching. After removal of 5,550 duplicates, 9,870 records were screened by title and abstract; 9,800 were excluded. Seventy full-text articles were assessed for eligibility; 66 were excluded based on predefined criteria. Four studies met inclusion criteria and were included in the final synthesis.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8355065/v1/df1c853e210f202bd8378292.png"},{"id":98437786,"identity":"fade48ad-5b99-4640-9da5-61b8727b9cae","added_by":"auto","created_at":"2025-12-17 16:57:47","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":673107,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8355065/v1/45a40d21-bc7a-42cd-a589-dc73aa73be90.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eSystematic Review: The Persistent Association Between Infant Antibiotic Exposure and Childhood Asthma After Accounting for Confounding by Indication and Reverse Causation\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eChildhood asthma is one of the most prevalent chronic pediatric conditions worldwide and arises from a complex interplay between genetic susceptibility and environmental exposures. Observational studies have repeatedly reported positive associations between antibiotic exposure in infancy and subsequent childhood asthma, prompting hypotheses that microbiome disruption during immune development may contribute to asthma pathogenesis. However, causal interpretation is complicated by two major biases: \u003cb\u003econfounding by indication\u003c/b\u003e, where antibiotics are prescribed for respiratory tract infections (RTIs) that independently increase asthma risk, and \u003cb\u003ereverse causation\u003c/b\u003e, where early asthma symptoms are misdiagnosed as infection and treated with antibiotics.\u003c/p\u003e \u003cp\u003eThis systematic review focuses on evidence that explicitly addresses these biases using advanced epidemiologic strategies, including sibling-matched designs and analyses adjusting for RTIs or excluding early wheezing.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"2. Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Search Strategy\u003c/h2\u003e \u003cp\u003eA systematic literature search was conducted in PubMed, Embase, Web of Science, and the Cochrane Library for studies published between January 2010 and \u003cb\u003eDecember 11, 2025\u003c/b\u003e. Search terms included combinations of \u003cem\u003eantibiotics\u003c/em\u003e, \u003cem\u003einfant\u003c/em\u003e, \u003cem\u003eearly life\u003c/em\u003e, \u003cem\u003echildhood asthma\u003c/em\u003e, \u003cem\u003econfounding by indication\u003c/em\u003e, \u003cem\u003ereverse causation\u003c/em\u003e, and \u003cem\u003esibling analysis\u003c/em\u003e. Reference lists of eligible studies and relevant reviews were manually screened.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Eligibility Criteria\u003c/h2\u003e \u003cp\u003eEligible publications included:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003ePrimary observational studies\u003c/b\u003e (cohort or case-control) evaluating antibiotic exposure during infancy (0\u0026ndash;24 months) and reporting physician-diagnosed asthma at \u0026ge;\u0026thinsp;4 years \u003cb\u003ewith explicit strategies to mitigate CbI and/or RC\u003c/b\u003e, including sibling-matched designs, exclusion of early wheezing, or explicit adjustment for respiratory tract infections; and/or\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eSystematic reviews/meta-analyses\u003c/b\u003e that explicitly evaluated the impact of CbI and/or RC mitigation (e.g., subgroup analyses restricted to studies addressing these biases).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003ePublications were excluded if they: (1) assessed asthma prior to age 4 as the primary outcome, (2) did not distinguish timing of antibiotic exposure in infancy, or (3) did not evaluate or stratify findings by approaches addressing CbI/RC.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Study Selection\u003c/h2\u003e \u003cp\u003eTwo reviewers screened titles/abstracts and full texts. Disagreements were resolved by consensus. Study selection is summarized in the PRISMA 2020 flow diagram (Fig.\u0026nbsp;1).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Data Extraction\u003c/h2\u003e \u003cp\u003eExtracted data included study design, population characteristics, exposure definition, asthma outcome definition, bias-mitigation methods (CbI/RC), and effect estimates (OR/HR) with confidence intervals.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Quality Assessment\u003c/h2\u003e \u003cp\u003ePrimary observational studies were assessed using the Newcastle\u0026ndash;Ottawa Scale. Systematic reviews/meta-analyses were assessed narratively for alignment with the objective and transparency of subgroup/sensitivity analyses addressing CbI/RC.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Data Synthesis\u003c/h2\u003e \u003cp\u003eDue to heterogeneity in study designs and analytical strategies, a narrative synthesis was performed, emphasizing comparisons between crude estimates, bias-adjusted meta-analytic estimates, and sibling-controlled analyses.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Study Characteristics\u003c/h2\u003e \u003cp\u003eFour eligible publications were included in the final synthesis (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Study selection is summarized in the PRISMA 2020 flow diagram (Fig.\u0026nbsp;1).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Evidence from Meta-Analyses Addressing CbI and RC\u003c/h2\u003e \u003cp\u003eZhang et al. (2021) reported a pooled crude association (OR 1.37; 95% CI, 1.29\u0026ndash;1.45) and demonstrated attenuation in analyses of studies that adjusted for CbI and RC (OR 1.19; 95% CI, 1.11\u0026ndash;1.28). Lu et al. (2023) similarly reported an attenuated but persistent association after bias adjustment in included studies.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Evidence from Sibling-Matched Designs\u003c/h2\u003e \u003cp\u003e\u0026Ouml;rtqvist et al. (2014) employed a nationwide sibling-matched cohort design. Associations observed in conventional cohort analyses for fetal exposure and non-respiratory indications were eliminated in sibling comparisons (fetal exposure HR\u0026thinsp;\u0026asymp;\u0026thinsp;0.99; non-respiratory indication HR\u0026thinsp;\u0026asymp;\u0026thinsp;0.85). In contrast, antibiotic exposure for respiratory indications remained associated with asthma in sibling analyses (HR 2.36), consistent with residual confounding by severity or type of underlying respiratory illness.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThis review indicates that much of the reported association between infant antibiotic exposure and childhood asthma is likely explained by confounding and reverse causation. Meta-analytic estimates attenuate when studies account for these biases, suggesting that crude associations overestimate any true effect. The strongest evidence comes from sibling-matched analyses demonstrating that familial confounding explains associations for fetal exposure and non-respiratory indications. The remaining association observed for respiratory-indication antibiotics likely reflects residual confounding by infection severity rather than a direct antibiotic effect.\u003c/p\u003e \u003cp\u003eAlthough antibiotic-driven microbiome disruption remains biologically plausible, current epidemiologic evidence does not strongly support a causal relationship. Future research should prioritize designs and analyses that more directly address unmeasured confounding and infection severity, including causal inference frameworks and longitudinal microbiome studies.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eContextual note (not included in synthesis)\u003c/strong\u003e \u003cp\u003eOkubo et al. (2021) evaluated antibiotic treatment during hospitalization for asthma exacerbation and was not included because it did not assess infant exposure (0\u0026ndash;24 months) leading to incident asthma at \u0026ge;\u0026thinsp;4 years.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"5. Limitations","content":"\u003cp\u003eThis review is limited by heterogeneity across included studies in exposure ascertainment, asthma diagnostic criteria, and the operationalization of bias-mitigation strategies. Publication bias is possible. Sibling-matched designs cannot account for non-shared factors such as individual-level differences in infection severity. Additionally, relatively few studies apply advanced causal inference methods, limiting definitive causal conclusions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"6. Conclusion","content":"\u003cp\u003eThe association between infant antibiotic exposure and childhood asthma is largely attributable to shared familial factors and residual confounding by respiratory illness severity. Evidence for a direct causal effect is limited. Rigorous causal inference studies are needed to clarify remaining uncertainties and to test microbiome-mediated mechanisms.\u003c/p\u003e "},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eZhang Z, Wang J, Wang H, Li Y, Jia Y, Yi M, Chen O. Association of infant antibiotic exposure and risk of childhood asthma: a meta-analysis. World Allergy Organ J. 2021;14(11):100607. https://pmc.ncbi.nlm.nih.gov/articles/PMC8661061/\u003c/li\u003e\n\u003cli\u003e\u0026Ouml;rtqvist AK, Lundholm C, Kieler H, Ludvigsson JF, Fall T, Ye W, Almqvist C. Antibiotics in fetal and early life and subsequent childhood asthma: nationwide population based study with sibling analysis. BMJ. 2014;349:g6979. https://www.bmj.com/content/349/bmj.g6979\u003c/li\u003e\n\u003cli\u003ePenders J, Vink C, Driessen GJ, London N, Thijs C, Stobberingh EE. Infant antibiotic use and wheeze and asthma risk: a systematic review and meta-analysis. Eur Respir J. 2011;38(2):295\u0026ndash;302. https://publications.ersnet.org/content/erj/38/2/295\u003c/li\u003e\n\u003cli\u003eLu Y, Li Z, Zhang Y. Early-life antibiotic exposure and childhood asthma: a systematic review and meta-analysis. Pediatr Pulmonol. 2023;58(3):1010\u0026ndash;1020. https://pmc.ncbi.nlm.nih.gov/articles/PMC9952656/\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003e\u003cstrong\u003eTable 1. Characteristics of Included Studies\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eStudy\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eCountry\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eDesign\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eSample Size\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eExposure Definition\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eAsthma Outcome Definition\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eCbI/RC Mitigation Approach\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eKey Findings / Notes\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eZhang et al., 2021\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMulti-country\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMeta-analysis\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026gt;1,000,000 (combined)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAntibiotic exposure in infancy (varied across included studies)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAsthma assessed ≥4 years (study-dependent)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eSubgroup analyses of studies addressing CbI/RC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCrude OR 1.37; bias-mitigated subgroup OR 1.19.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eÖrtqvist et al., 2014\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eSweden\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePopulation-based cohort + sibling-matched\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.8 million\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eFetal and early-life antibiotics; indication-stratified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eChildhood asthma\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eSibling matching; infection-related controls\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAssociation eliminated for fetal/non-respiratory; persistent for respiratory indications (HR 2.36).\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003ePenders et al., 2011\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNetherlands\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eSystematic review/meta-analysis\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e22 studies\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eInfant antibiotic exposure\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eWheeze/asthma (varied); asthma commonly ≥5 yrs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eInfection adjustment in included studies\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eProvides contextual pooled evidence; susceptibility to residual confounding acknowledged.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eLu et al., 2023\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eChina\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eSystematic review/meta-analysis\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e34 studies\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEarly-life antibiotic exposure\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eChildhood asthma (commonly ≥5 yrs)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAdjusted analyses for RTIs/early wheeze\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAttenuated but persistent association after adjustment.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eNote: Table includes both primary observational studies and systematic reviews/meta-analyses that explicitly addressed confounding by indication and/or reverse causation.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"antibiotics, asthma, infancy, confounding by indication, reverse causation, sibling analysis, epidemiology","lastPublishedDoi":"10.21203/rs.3.rs-8355065/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8355065/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eEarly-life antibiotic exposure has been repeatedly associated with an increased risk of childhood asthma. However, this association is vulnerable to substantial methodological bias, particularly confounding by indication (CbI) and reverse causation (RC). This systematic review evaluates whether the association persists in studies employing advanced epidemiologic methods designed to mitigate these biases.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eA systematic search of PubMed, Embase, Web of Science, and the Cochrane Library was conducted from January 2010 through \u003cb\u003eDecember 11, 2025\u003c/b\u003e. Eligible publications included (1) primary observational studies (cohort or case-control designs) evaluating antibiotic exposure during infancy (0\u0026ndash;24 months) and physician-diagnosed asthma at \u0026ge;\u0026thinsp;4 years, and/or (2) systematic reviews/meta-analyses that explicitly evaluated or stratified results by approaches addressing CbI and/or RC (e.g., adjustment for respiratory tract infections, exclusion of early wheezing, or comparable bias-mitigation strategies). Study selection followed PRISMA 2020 guidelines. Methodological quality was assessed using the Newcastle\u0026ndash;Ottawa Scale for primary studies; systematic reviews were assessed narratively for relevance to the review objective.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eFour eligible studies were included. Crude observational estimates reported in meta-analytic syntheses demonstrated a strong association (pooled OR\u0026thinsp;\u0026asymp;\u0026thinsp;1.37). In analyses explicitly addressing CbI and RC, estimates attenuated but remained statistically significant (pooled OR 1.19; 95% CI, 1.11\u0026ndash;1.28). In contrast, a nationwide sibling-matched cohort study eliminated the association for fetal exposures and non-respiratory indications, suggesting substantial familial confounding. A persistent association remained only for antibiotics prescribed for respiratory infections (sibling-matched HR 2.36), consistent with residual confounding by illness severity.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eThe association between infant antibiotic exposure and childhood asthma is largely explained by shared familial factors and residual confounding related to respiratory illness severity rather than a direct causal effect of antibiotics. While biological plausibility via gut microbiome disruption remains, current epidemiologic evidence does not strongly support causality. Further studies using advanced causal inference methods are warranted.\u003c/p\u003e","manuscriptTitle":"Systematic Review: The Persistent Association Between Infant Antibiotic Exposure and Childhood Asthma After Accounting for Confounding by Indication and Reverse Causation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-16 14:13:53","doi":"10.21203/rs.3.rs-8355065/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f09318bf-d2c8-4ff6-b056-c86583568c75","owner":[],"postedDate":"December 16th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-12-16T14:13:53+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-16 14:13:53","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8355065","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8355065","identity":"rs-8355065","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}