Suppression of the COVID-19 outbreak in the municipality of Vò, Italy
Analysis of the early COVID-19 outbreak in the municipality of Vò, Italy.
Jefferson T, Heneghan C.
Published on June 6, 2020
Transmission Dynamics of COVID-19
||Lavezzo E, Franchin E, Ciavarella C, et al. Suppression of COVID-19 outbreak in the municipality of Vo, Italy. medRxiv:2020.04.17.20053157. 2020
||Public, from 21 February 2020
||Person to person
In one of the two original epicentres of the outbreak in Northern Italy, Vò Euganeo, cases were infected in the community before lockdown, or subsequently from asymptomatic infected people living in the same household.
- 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%)
- 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.
- 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.
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).
What did they do?
The study took place between 23rd February 2020 and 8th March 2020, in the town of Vò Euganeo, one of the two synchronous epicentres of the outbreak in Northern Italy. Vò is a discrete town which was isolated from the outside by the first localised lockdowns in Italy. Thus the authors had a discrete denominator without outside movement. They studied dynamics and tested 85.9% and 71.5% of the stratified sample of the eligible population in two phases with nasopharyngeal swabs around 2 weeks apart. They assessed the prevalence and progression of asymptomatic and viral loads.
The number of infected cases was small, in a total test population of under 3,000. The test only looked for active infection so there is the possibility that some of the individuals had been infected previously.
|Clearly defined setting
||Demographic characteristics described
||Follow-up length was sufficient
||Transmission outcomes assessed
||Main biases are taken into consideration
What else should I consider?
The authors are carrying out further follow up studies including genetic sequencing to assess any association with susceptibility to infection and serological surveys to define with certainty the infection status of different age groups. No children who took part in the study tested positive for infection despite at least 13 living with an infected family member; whereas there was a chance of an adult becoming infected when living together with infected family members.
About the authors
Carl is Professor of EBM & Director of CEBM at the University of Oxford. He is also a GP and tweets @carlheneghan. He has an active interest in discovering the truth behind health research findings
Tom Jefferson, epidemiologist.