Researchers in Italy have reported on the success of the contact tracing efforts made to control the coronavirus disease 2019 (COVID-19) outbreak in the province of Trento during phase I (March to April) of the epidemic.
The contact tracing involved new software that enabled the surveillance of people who had been in contact with infected individuals and rapidly identified links between cases and contacts.
Mariagrazia Zuccali (Department of Prevention, Provincial Agency for Health Services, Trento) and colleagues say the lockdown measures, closure of non-essential services, and isolation of infection cases and contacts in Italy during phase I of the COVID-19 outbreak has successfully flattened the curve of the epidemic.
However, the team’s report on the contact tracing carried out in Trento has highlighted areas of concern, as activities and movements gradually return to normal in the country.
The researchers identified a high risk of infection associated with workplace contacts, for example, and warn that the management of companies and factories during phase II of reopening will be of fundamental importance in controlling the epidemic.
Of all age groups included in the study, the highest rate of contagiousness was seen among children aged 0 to 14 years, a finding that the researchers say supports a policy of maximum caution in the reopening of primary schools.
The team also says the study highlights the importance of ensuring contact tracing is supported by suitable monitoring tools that will enable effective management of contacts and timely analysis of disease spread.
A pre-print version of the paper is available on the medRxiv* server, while the article undergoes peer review.
Trento was profoundly affected during phase I
The autonomous province of Trento in northern Italy was severely affected by the COVID-19 outbreak during phase I of the epidemic. Although full lockdown began on March 10th, the number of cases continued to rise through the remainder of March and reached a plateau in April.
The Provincial Agency for Health Services (APSS) led the implementation of contact tracing shortly after the first cases of COVID-19 were identified in the province.
However, Zuccali and the team say the data collection methods did not always include adequate information on the number of contacts under surveillance, the relationship between cases and contacts, the number of contacts who had become cases, and the start and end dates of follow-up surveillance.
To standardize data collection and provide a database for more detailed epidemiological analysis, the researchers developed a contact tracing website that included geolocation components and showed links between cases and contacts using open-source software.
What did the study find?
The researchers report that during phase I of the epidemic when Trento was mostly under lockdown, 2,812 people with laboratory-confirmed infections had 6,690 community contacts. Of the 6,690 contacts, 890 (13.3%) developed symptoms and became cases themselves, giving a secondary attack rate of 13.3%.
The risk of a contact developing symptoms increased with age, with the rate as low as 8.4% among children aged 0 to 14 years and as high as 18.9% in those older than 75 years.
The most significant risk of transmission to contacts was identified among 14 cases aged 0 to 14 years. Eleven (22.4%) of the 49 contacts these children had also become cases, which was the highest rate of contagiousness among all age groups included in the study.
The lowest rate of transmission to contacts was among people aged 30-49 years (10.6%), with rates among those over 50 years increasing with older age.
“Although childhood contacts were less likely to become cases, children were more likely to infect household members, perhaps because of the difficulty of successfully isolating children in household settings,” writes the team. “Overall, our data are therefore in support of a policy of maximum caution concerning the reopening of children’s communities and primary schools.”
Workplace exposure was riskier than living with a case
Workplace exposure was associated with a higher risk of becoming a case than living with a case or having a non-cohabiting family member or a friend who was a case.
The researchers say workplace exposure was an infrequent method of contact during the lockdown period. However, “it will be of fundamental importance in phase II of reopening. What happens inside factories and companies is likely to be of considerable importance to controlling the epidemic,” they add.
Overall, during March and April, 606 outbreaks were identified, the vast majority of which (74%) were only made up of two cases. Sixteen percent of outbreaks consisted of three cases, 6.8% consisted of four cases and 3% were made up of five or more cases (maximum of eight).
Protection will be lacking as lockdown relaxes
“The combination of physical spacing measures (lockdown), closure of non-essential activities and identification of cases and contacts with consequent treatment, and isolation and quarantine in Italy during phase I has allowed us to flatten the epidemic curve,” write Zuccali and colleagues.
However, the gradual relaxation of intervention measures during phase II will mean protection is lacking, they say.
“The only real possibility to block the chains of infection consists of selective and timely isolation of new cases and quarantine of their contacts.”
The researchers say this will be especially important once the number of contacts per case starts to rise as people become freer to move about.
“Contact tracing and monitoring activities must be facilitated and supported through suitable monitoring tools, which facilitate both contact management and timely epidemiological analysis,” they conclude.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.