Evidence Summary

Positive rates:

• 73  out of the 2,812 subjects tested at the first time-point were positive: prevalence 2.6% (95% CI  2.1 to 3.3%).
• At the second time point 29  total  positive cases were identified: prevalence 1.2% (95%  CI  0.8 to 1.8%), with 8  new  cases  (0.3%;  95%  CI  0.15-0.7%)

Asymptomatic rates:

• 30 out of the 73 positive individuals, 41%; (95% CI 30 to 53%) – at the first survey were asymptomatic. At the second survey 13 out of 29 positives were asymptomatic, 45% (95%  CI  27 to 64)

Three out of eight individuals with new infections identified in the second survey had mild  symptoms and did not require hospitalization. Some had contact with asymptomatics. The other five had no symptoms despite two sharing the same flat with symptomatic infected relatives, one reported meeting an asymptomatic infected individual before the lockdown and one had no contact with positive individuals. The last subject shared the same flat with two asymptomatic relatives. All asymptomatic individuals never developed symptoms, in the interval between the first and the second survey, and a high proportion of them cleared the infection.

Pre-symptomatic transmission:

• the authors report a cluster of infection traceable to a presymptomatic relative.

None of the 234 tested children (aged 0 to 10 years) was positive; at least 13 of these children were living with an infected relative. Older people had three times the prevalence of infection than older people.

Household transmission:

The relative risk of contracting the infection having an infected relative living in the same household gave an odds ratio of 84.5 (95% CI 16.8 to 425.4).