Describing the epidemic trends of COVID-19 in the area covered by Agency for Health Protection of the Metropolitan Area of Milan.

Tunesi, Sara; Murtas, Rossella; Riussi, Antonio; Sandrini, Monica; Andreano, Anita; Greco, Maria Teresa; Gattoni, Maria Elena; Guido, Davide; Gervasi, Federico; Consolazio, David; Adreoni, Laura; Decarli, Adriano; Bergamaschi, Walter; Russo, Antonio Giampiero

OBJECTIVES to describe the epidemic trends of COVID-19 over time and by area in the territory covered by Milan's Agency for Health Protection (ATS-MI) from February to May 2020. DESIGN descriptive study of COVID-19 cases. SETTING AND PARTICIPANTS a new information system was developed to record COVID-19 cases with positive nasopharyngeal swab. Patients resident in the area covered by ATS-MI with symptom onset between February and May 2020 were selected. Different epidemic periods were considered based on the timeline of the various regional and national containment measures. MAIN OUTCOME MEASURES case fatality ratios, incidence rates, and reproduction number by epidemic period and sub-area of ATS-MI. RESULTS a total of 27,017 swab-positive COVID-19 cases were included. Mean age was 65 years and males were 45%. Incidence in the ATS-MI area was 776 per 100,000 population. The number of deaths was 4,660, the crude case fatality ratio was 17.3%, higher in males (21.2%) than in females (14.0%). The estimated reproduction number registered its peak (3.0) in the early stages of the epidemic and subsequently decreased. Territorial differences were observed in the epidemic spread, with a higher incidence in the Lodi area. CONCLUSIONS estimated incidence and case fatality ratios were higher than national estimates for Italy. Each ATS-MI area had different epidemic spread patterns.