Excess cases of influenza-like illnesses synchronous with coronavirus disease (COVID-19) epidemic, France, March 2020.

April 9, 2020

Boëlle P., Souty C., Launay T., et al

Eurosurveillance

Several French regions where coronavirus disease (COVID-19) had reported a renewed increase in Influenza-like illnesses (ILI) cases and acute respiratory infections (ARI) in general practice. ILI exhibits fever of sudden onset (>39°C) with respiratory signs like coughing, running nose and myalgia; ARI includes any disease with respiratory signs and are only monitored in people older than 65 years, unlike ILI. Nasopharyngeal swabs in one ILI case and up to two ARI cases per week were taken for viral characterisation and the causes may be Influenza virus, respiratory syncytial virus, human rhinovirus, human metapneumovirus and now SARS-CoV-2. The ILI incidence showed renewed increase with 33 consultations per 100,000 in excess during week 9 and with 84 consultations per 100,000 in excess in week 10. Assuming exponential growth (typical of early epidemics) from week 8 to 10, 2020. We found that the excess number of cases had an exponential growth rate per week of 0.69. Characteristics of the influenza season, change in population behaviour and increase in COVID19 incidence may have contributed to this, especially because of the similarities between COVID-19 and influenza symptoms. Estimating the true number of COVID-19 cases can only be tentative at this early stage of the epidemic with data from a non-dedicated surveillance system. It is likely that the case definition of ILI does not allow identifying all COVID-19 cases.

Boëlle, P. Souty, C. Launay, T. Excess cases of influenza-like illnesses synchronous with coronavirus disease (COVID-19) epidemic, France, March 2020. Euro surveillance 2020; 25(14).

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