Contact tracing and isolation of asymptomatic spreaders to successfully control the COVID-19 epidemic among healthcare workers in Milan (Italy)

Mandić‐Rajčević, Stefan; Masci, Federica; Crespi, E; Franchetti, Sara; Longo, Anna; Bollina, Ilaria; S, Velocci; Amorosi, A.; Baldelli, Roberto; Boselli, L; Negroni, L; A, Zà; Nv, Orfeo; Ortisi, G; Colosio, Claudio

doi:10.1101/2020.05.03.20082818

Cited by 13 publications

(16 citation statements)

References 17 publications

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“…In the Milan area, Northwestern Italy, 10% positive swabs were reported in the framework of contact tracing; no mass screening was carried out. Overall, 2.6% of positive cases were reported after "random testing" in HW [34].…”

Section: Discussionmentioning

confidence: 99%

Health Surveillance and Response to SARS-CoV-2 Mass Testing in Health Workers of a Large Italian Hospital in Verona, Veneto

Porru

Carta

Monaco

et al. 2020

IJERPH

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Italy presented the first largest COVID-19 outbreak outside of China. Veneto currently ranks fourth among the Italian regions for COVID-19 confirmed cases (~19,000). This study presents health surveillance data for SARS-CoV-2 in 6100 health workers (HW) employed in a large public hospital. Workers underwent oropharyngeal and nasopharyngeal swabs, with a total of 5942 participants (97.5% of the population). A total of 11,890 specimens were tested for SARS-CoV-2 infection using PCR, identifying the viral genes E, RdRP, and N. Positive tests were returned for 238 workers (cumulative incidence of 4.0%, similar in both COVID and nonCOVID units). SARS-CoV-2 risk was not affected by gender, age, or job type, whereas work setting and occupation were both predictors of infection. The risk was higher in medical wards (OR 2.7, 95% CI 1.9–3.9) and health services (OR 4.3, 95% CI 2.4–7.6), and lower in surgical wards and administration areas. To our knowledge, this study represents the largest available HW case list swab-tested for SARS-CoV-2, covering almost the total workforce. Mass screening enabled the isolation of HW, improved risk assessment, allowed for close contacts of and infected HW to return to work, provided evidence of SARS-CoV-2 diffusion, and presented solid ground to prevent nosocomial SARS-CoV-2 infections. The ongoing concurrent sero-epidemiological study aims to enable the improvement of health surveillance to maintain the safety of HWs and the communities they serve.

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Section: Discussionmentioning

confidence: 99%

Health Surveillance and Response to SARS-CoV-2 Mass Testing in Health Workers of a Large Italian Hospital in Verona, Veneto

Porru

Carta

Monaco

et al. 2020

IJERPH

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“…In a study carried out in Milan on a large population including 5700 HCWs, the rate of positive nasopharyngeal swab was 10%, whereas the proportion of positive results was only 2.6% through random tested HCWs [12]. The lower proportion of positive HCWs identified in our study might be due both to misclassification of close contacts (some operators might have intentionally over reported the duration of the contact to receive the diagnostic swab) and to the lower incidence rate in the general population of Rome, compared to that of Milan in the same period.…”

Section: Discussionmentioning

confidence: 99%

Contact Screening for Healthcare Workers Exposed to Patients with COVID-19

Coppeta

Somma

Ippoliti

et al. 2020

IJERPH

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In China and Italy, many cases of coronavirus disease 2019 (COVID-19) have occurred among healthcare workers (HCWs). Prompt identification, isolation and contact tracing of COVID-19 cases are key elements in controlling the COVID-19 pandemic. The aim of this study was to evaluate the rate of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection among HCWs exposed to patients with COVID-19 in relation to the main determinants of exposure. To assess the risk of exposure, we performed active symptom monitoring in 1006 HCWs identified as contacts of COVID19 cases. The presence of symptoms was statistically associated with a positive nasopharyngeal swab result. Only one subject was asymptomatic at the time of positive test. These data suggest that clinical history may help in the selection of subjects to be investigated by means of reverse transcriptase-polymerase chain reaction (RT-PCR) in the case of a shortage of diagnostic resources. We found that close contact (within 2 m for 15 min or more) was not statistically related to contagion. Regarding the use of personal protective equipment (PPE), only the use of facial masks was inversely related to the chance of becoming infected (p < 0.01). In conclusion, our data show that unprotected contacts between HCWs should be considered a major route of HCW contagion, suggesting that the use of facial masks should be implemented even in settings where known patients with COVID-19 are not present.

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“…Of the 19 studies included, contact tracing of index patients who were identified as asymptomatic cases, according to our definition, was reported in nine (Table 1, Figure 1) (6,11,(19)(20)(21)(22)(23)(24)(25)). All except one tested all close contacts for SARS-CoV-2, regardless of symptoms (23 (21).…”

Section: Summary Of Secondary Attack Rates Of Asymptomatic Index Casesmentioning

confidence: 99%

Defining the role of asymptomatic SARS-CoV-2 transmission – a living systematic review

Qiu

Nergiz

Maraolo

et al. 2020

Preprint

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Background Reports suggest that asymptomatic individuals (those with no symptoms at all throughout the infection) with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are infectious, but the extent of asymptomatic transmission requires further understanding. Purpose This living review aims to critically appraise available data about secondary attack rates from people with asymptomatic and pre-symptomatic SARS-CoV-2 infection. Data sources Medline, EMBASE, China Academic Journals full-text database (CNKI), and pre-print servers were searched from 30 December 2019 to 3 July 2020 using relevant MESH terms. Study selection Studies that report on contact tracing of index cases with asymptomatic or pre-symptomatic SARS-CoV-2 infection, in either English or Chinese were included. Data extraction Two authors independently extracted data and assessed study quality and risk of bias. We calculated the secondary attack rate as the number of contacts with SARS-CoV-2, divided by the number of contacts tested. Data synthesis Of 928 studies identified, 19 were included. Secondary attack rates from asymptomatic index cases ranged from 0% to 2.8% (9 studies). Pre-symptomatic secondary attack rates ranged from 0.7% to 31.8% (10 studies). The highest secondary attack rates were found in contacts who lived in the same household as the index case. Other activities associated with transmission were group activities such as sharing meals or playing board games with the index case. Limitations We excluded some studies because the index case or number of contacts were unclear. Owing to the anticipated heterogeneity, we did not produce a summary estimate of the included studies. Conclusion Asymptomatic patients can transmit SARS-CoV-2 to others, but our findings indicate that such individuals are responsible for fewer secondary infections than people with symptoms in the same studies. Systematic review registration PROSPERO CRD42020188168 Funding: No funding was received

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Contact tracing and isolation of asymptomatic spreaders to successfully control the COVID-19 epidemic among healthcare workers in Milan (Italy)

Cited by 13 publications

References 17 publications

Health Surveillance and Response to SARS-CoV-2 Mass Testing in Health Workers of a Large Italian Hospital in Verona, Veneto

Health Surveillance and Response to SARS-CoV-2 Mass Testing in Health Workers of a Large Italian Hospital in Verona, Veneto

Contact Screening for Healthcare Workers Exposed to Patients with COVID-19

Defining the role of asymptomatic SARS-CoV-2 transmission – a living systematic review

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