Outbreaks of infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in healthcare centers may often originate from transmission among healthcare workers, not patients, according to data published in Antimicrobial Resistance and Infection Control.

Investigators at the Charité-University Medicine hospital in Berlin, Germany, used contact tracing to collect data on 4 outbreaks from March 1 to April 30, 2020. They defined a healthcare-associated outbreak as two or more healthcare workers with a positive SARS-CoV-2 reverse transcriptase polymerase chain reaction (RT-PCR) test result that had a likely SARS-CoV-2 epidemiological link and an assumed acquisition in the healthcare setting. Contact tracing was conducted for a period of 48 hours before symptom onset or, in the case of asymptomatic infections, 48 hours before sample collection.

Four healthcare-associated outbreaks were detected among 24 people: 23 healthcare workers and 1 patient, suggesting that most SARS-CoV-2 infections were caused by transmission from healthcare worker to healthcare worker. Outbreaks occurred in the departments of nephrology and dialysis (n=9), anesthesiology (n=8), surgical pediatrics (n=4), and neurology (n=3).

Infection control measures were taken to contain the outbreaks, such as isolation, SARS-CoV-2 testing, and mask wearing. Outbreaks were considered contained if no new cases developed for a period of 28 days; this was achieved for all 4 outbreaks.

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Study limitations included lack of molecular typing of SARS-CoV-2 strains to meticulously reconstruct chains of infection, not testing all healthcare workers in the entire hospital, possible false negative results, and possible inconsistent compliance with infection control measures between individuals. Healthcare workers also may not have answered questions accurately about proper use of personal protective equipment (PPE) or given a full list of unprotected contacts for fear of negative consequences.

Out of all the infection control measures taken, required mask-wearing for all healthcare workers was most effective against the spread of SARS-CoV-2 according to study authors. They noted that no new infections occurred in the nephrology and dialysis department, or the entire campus, after the hospital required continuous mask-wearing starting March 25, 2020.

Since many healthcare workers underestimate the chance of transmission among colleagues, unprotected contacts often occurred during lunch and smoking breaks, when workers were away from patients and their masks were taken off. In conclusion, there needs to be an increased awareness of internal transmission among healthcare workers as a key focus in the battle against COVID-19.


Schneider S, Piening B, Nouri-Pasovsky PA, Krüger AC, Gastmeier P, Aghdassi SJS. SARS-Coronavirus-2 cases in healthcare workers may not regularly originate from patient care: lessons from a university hospital on the underestimated risk of healthcare worker to healthcare worker transmission. Antimicrob Resist Infect Control. 2020;9(1):192. doi:10.1186/s13756-020-00848-w