Abstract
We investigated a COVID-19 outbreak at a fire station in Marseille, France. Confirmed cases were defined as individuals with positive SARS-CoV-2 reverse transcription (RT)-PCR and/or neutralising antibodies. All 85 firefighters at work during the outbreak period were included after questioning and sampled for RT-PCR and viral neutralisation assay. Twenty-three firefighters were confirmed positive, 19 of them were symptomatic, and four asymptomatic cases were confirmed by virus neutralisation. A total of 22 firefighters had specific neutralising antibodies against SARS-CoV-2. Neutralising antibodies were found in four asymptomatic and 18 symptomatic cases. Eleven symptomatic cases had high titres (≥ 1:80). The earliest detection of neutralising antibodies was 7 days after symptom onset, and 80% had neutralising antibodies 15 days after onset. One viral culture was positive 13 days after onset. The attack rate was 27%. We identified two introductions of the virus in this outbreak, through a presymptomatic and a paucisymptomatic case. Asymptomatic cases were not the source of a third generation of cases, although they worked without wearing a mask, indicating that asymptomatic cases did not play a significant role in this outbreak. Management and strategy based on early research of clinical signs associated with self-quarantine was effective.
Highlights
Complete investigations of coronavirus disease (COVID19) outbreaks in close-contact communities such as fire stations are scarce
We describe the outbreak investigation, the chain of SARS-CoV-2 transmission, and the workplace safety plan implemented at the fire station to contain the spread of the virus
The six other symptomatic individuals were confirmed at the time of the investigation: one with a positive reverse transcription (RT)-PCR test, one with both a positive reverse transcription PCR (RT-PCR) test and neutralising antibodies, and four only by virus neutralisation
Summary
Complete investigations of coronavirus disease (COVID19) outbreaks in close-contact communities such as fire stations are scarce. Such a context offers the opportunity to track virus transmission and increase knowledge of COVID-19 epidemiology. It was suspected that presymptomatic (i.e. detection of the virus before symptom onset) as well as asymptomatic (i.e. detection of the virus without any symptoms) individuals were able to transmit the virus and can play a role in the transmission chain [3,4]. Cellular and humoral immune responses are induced [6,7] The latter can be measured with serological assays, and neutralising antibodies appear in the 2 weeks following infection. Until more data are available, it is commonly accepted that the presence of neutralising antibodies leads to clinical protection from reinfection with the same strain [9,10]
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