key: cord-298441-77w86l8q
authors: Lombardi, Andrea; Consonni, Dario; Carugno, Michele; Bozzi, Giorgio; Mangioni, Davide; Muscatello, Antonio; Castelli, Valeria; Palomba, Emanuele; Cantù, Anna Paola; Ceriotti, Ferruccio; Tiso, Basilio; Pesatori, Angela Cecilia; Riboldi, Luciano; Bandera, Alessandra; Lunghi, Giovanna; Gori, Andrea
title: Characteristics of 1,573 healthcare workers who underwent nasopharyngeal swab for SARS-CoV-2 in Milano, Lombardy, Italy
date: 2020-06-20
journal: Clin Microbiol Infect
DOI: 10.1016/j.cmi.2020.06.013
sha: 
doc_id: 298441
cord_uid: 77w86l8q

OBJECTIVES: The management of healthcare workers (HCWs) exposed to confirmed cases of COVID-19 is still a matter of debate. We aimed to assess in this group the attack rate of asymptomatic carriers and the symptoms most frequently associated with the infection. METHODS: Occupational and clinical characteristics of HCWs who performed a nasopharyngeal swab for the detection of SARS-CoV-2 in a University Hospital from February 24, to March 31, 2020, were collected. For those who tested positive and for the asymptomatic positives we checked laboratory and clinical data as of May 22 to calculate the time necessary to become test-negative and to verify whether symptoms developed thereafter. Frequencies of positive tests were compared according to selected variables using multivariable logistic regression models. RESULTS: Positive tests were 139 among 1,573 HCWs (8.8%, 95% confidence interval [CI]: 7.5-10.3), with a marked difference between symptomatic (122/503, 24.2%) and asymptomatic (17/1,070, 1.6%) workers (p<0.001). Physicians were the group with the highest frequency of positive tests (61/582, 10.5%), whereas clerical workers and technicians displayed the lowest frequency (5/137, 3.6%). The likelihood of being positive increased with the number of reported symptoms and the strongest predictors were taste and smell alterations (odds ratio [OR]= 76.9) and fever (OR = 9.12). The median time from first positive test to a negative test was 27 days (95% CI: 24-30). CONCLUSIONS: A relevant number of HCWs can be infected by SARS-CoV-2 without displaying any symptom. Among symptomatic workers, the key symptoms to guide diagnosis are taste and smell alterations and fever. In median, almost four weeks are necessary to achieve negativity of nasopharyngeal swab.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a previously unknown 48 virus which recently jumped from a not yet identified animal host to humans and it is 49 responsible of coronavirus disease 2019 . 1 The virus has now spread worldwide 50 from China, causing the first pandemic of the XXI century, disrupting health-care services in 51 the affected countries and exacting a terrific toll of human lives. 2-3 52 Healthcare workers (HCWs) are a crucial actor in the pandemic. Indeed, they are acting in an 53 emergency situation and are continuously at risk of being infected. At the same time, they are 54 in contact with the most fragile elements of our society, those who need health assistance. It 55 is therefore mandatory to avoid that infected HCWs act as spreaders of the disease. 56 Unfortunately, it is still unclear which microbiologic investigations and procedures should be 57 adopted toward HCWs in COVID-19 settings, especially to those exposed to confirmed cases 58 of COVID-19 and at risk for infection. To answer this question, we reviewed all the 59 nasopharyngeal swab performed in HCWs exposed to confirmed cases of COVID-19 at the 60 Foundation IRCCS Ca' Granda Ospedale Maggiore Policlinico located in Milan, the capital 61 of Lombardy, by large the Italian region mostly affected by We assessed 62 frequency of positive tests among symptomatic and asymptomatic HCWs and evaluated the 63 association between occupation, symptoms (type and number), and presence of the infection.

Furthermore, we also calculated the median time between the day of diagnosis (first positive test) and the day in which the HCW became test-negative.

We collected occupational and clinical characteristics of all the consecutive HCWs who We tested HCWs at risk for infection, which is defined as a contact with a patient or another 74 HCW with (or later diagnosed with) SARS-CoV-2 infection. All those at risk were, according 75 to the internal protocol, identified and contacted by the hospital infection prevention unit, 76 isolated at home and tested. HCWs were subdivided into physicians (including residents), 77 nurses and midwives, healthcare assistants, health technicians, and clerical workers and 78 technicians. All the information was collected by the infectious disease notification form 79 associated to each test. Workers were defined as symptomatic if presented any of the 80 following in the 14 days preceding the test: fever, cough, dyspnoea, asthenia, myalgia, 81 coryza, sore throat, headache, ageusia or dysgeusia, anosmia or parosmia, ocular symptoms, men (three physicians and two nurses) and three women (two physicians and a clerical 144 worker) were hospitalized.

A minority of the HCWs (81/1,537, 5.3%) reported to have had a contact with an infected 146 person outside the hospital (relatives, colleague, or friends). Of these, 12/81 (14/81, 8.7%) 147 were found to be positive.

In this Italian group of HCWs exposed to confirmed cases of COVID-19, the presence of 150 symptoms, and particularly taste and smell alterations and fever, was associated with Interestingly, the AUC of a model considering six groups of symptoms (fever, myalgia, 155 asthenia, ocular symptoms, dyspnoea, and taste and smell alterations) was 0.83. Based on 156 these results, it seems reasonable to tailor the screening approach of HCWs at risk based on 157 the resources available. In low-resource settings we suggest focusing to test those with 158 symptoms to maximize efficacy, especially considering the continuous exposure of HCWs to 159 at risk situations, thus requiring repeated testing sessions. Nevertheless, it should be 160 underlined that in our study a non-negligible number of workers were infected but displayed 161 no symptoms, meaning that a fraction of those infected can be lost with a symptoms-based 162 screening strategy. Therefore, in middle-and high-resource settings a mass screening for all 163 HCWs exposed to confirmed COVID-19 cases appears the best approach to limit the spread When stratified according to occupation, test-positive frequencies were clearly higher among 177 subsets with direct contact with patients (physicians including residents, nurses and 178 midwives, healthcare assistants and health technicians) than those without (clerical works and 179 technicians). Consequently, careful screening of these groups of workers should be 180 mandatory. No differences in terms of infection attack rate were seen between different age 181 groups nor between men and women, suggesting that risk factors for acquiring COVID-19 182 among HCWs are unrelated to age and sex.

Another relevant point is the significant number of HCWs who were negative at the first test 184 but resulted positive when tested a second time. This might represent a serious concern, as a 185 discrete fraction of those can further spread the virus unnoticed, thus hampering the efficacy 186 of the screening strategy. It should be noted, however, that the second test was performed on 187 a small number of operators and not on a routine basis, making these considerations subject 188 to several potential biases. In addition, in a relevant proportion of our population we could 189 not retrieve information about the most likely date of exposure to a documented case. Thus, we cannot exclude a recent contact in which case the first test may have been performed too early (i.e. still in the incubation period which has been estimated to be five 192 days), before a sufficient amount of viral particles is detectable in the nasopharynx. 8

Moreover, it has to be considered that HCWs employed in COVID-19 units/hospitals are at 194 risk of SARS-CoV-2 exposure on a daily basis and therefore repeated exposures, even 195 unnoticed, can occur also after the first one who motivated the test. Moreover, technical 196 limitation can be responsible of falsely negative test, considering that the sensitivity of 197 nasopharyngeal swab for SARS-CoV-2 detection has been estimated to be around 71%. 9

Finally, we observed a median time from first positive test to a negative test of 27 days. This 

Our study has some limitations. First, the surveillance system was quickly set-up in a few 206 days due the virus spread in our region since February 20, when the first Italian case was 207 identified in the south-east part of Lombardy. Therefore, data quality was imperfect and 208 extensive time-consuming data editing (through review of electronical records and, when 209 necessary, of paper forms) was required to retrieve and complete the relevant information.

For the same reason, and because we wanted to provide a rapid response to concerns about 211 virus spread in the hospital, we were forced to limit the analyses to only a part of the work- 

World Health Organization (WHO), COVID-19 definitions