Descrizione dell’andamento dell’epidemia di COVID-19 nell’ATS di Milano [Describing the epidemic trends of COVID-19 in the area covered by Agency for Health Protection of the Metropolitan Area of Milan]

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.