Decreased neutrophil phagocytosis and killing of bacteria in COVID-19 patients

A new coronavirus disease was described in December 2019 (COVID-19) in Wuhan City, Hubei Province, China and has reached pandemic status. According to the World Health Organization, the incubation time from being infected to symptom emergence averages 5-6 days for COVID-19 but can be up to 14 days. The mortality rate varies in different countries but is greater in elderly people and in patients with cardiovascular disease, diabetes and chronic respiratory diseases. Patients with chronic respiratory diseases often have reduced neutrophil function. We sought to measure neutrophil phagocytosis and bacterial killing in COVID-19 patients. 30 COVID-19 patients and 9 healthy individuals were recruited from the Masih Daneshvari Hospital (Tehran, Iran) from March-May 2020. Polymorphonuclear (PMN) cells were isolated from whole fresh blood and incubated with green fluorescent protein (GFP) labelled methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa. Phagocytosis was determined by measuring the florescence of co-cultures of bacteria and neutrophils and reported as the lag time before exponential growth. The number of viable bacteria was determined after 70 h by the Colony-Forming Unit (CFU). Bacterial phagocytosis of SA (22±0.9 versus 9.2±0.5h, p<0.01) and PA (12.4±0.6 versus 4.5±0.22, p<0.01) was significantly reduced in COVID-19 patients compared with healthy control subjects. After 70h there was a significant increase in CFU in COVID-19 subjects compared with healthy control subjects for both SA (2.6±0.09 x 10 8 versus 0.8±0.04 x 10 8 CFU/ml, p<0.001) and PA (2.2±0.09 x 10 9 versus 1.0±0.06 x 10 9 CFU/ml, p<0.001).These results suggests a defect in bacterial clearance by neutrophils in COVID-19 patients.