To the Editor—Since the beginning of the coronavirus disease 2019 (COVID-19) epidemic in France in March 2020, laboratories have had to reorganize to implement COVID-19 diagnosis at a large scale. In this context, the handling of samples from suspected COVID-19 patients can expose laboratory staff to severe acute respiratory coronavirus virus 2 (SARS-CoV-2). The protection of healthcare workers (HCWs) is a critical point for pandemic control, at an individual level for care continuity and at a collective scale to avoid transmission to their contact cases. ^{Reference Kea, Johnson and Lin1} Guidelines for respiratory- or stool-sample handling have recommended wearing filtering facepiece respirator 2 (FFP-2) mask, double pairs of gloves, and a disposable gown. After the first pretreatment in a microbiological safety station, samples need further biological inactivation before viral RNA extraction and genome amplification for SARS-CoV-2 detection.

In our laboratory, the number of SARS-CoV-2 RT-PCR tests increased gradually, from 20 analyses per day in February 2020 to 1,500 per day by the end of April 2020. The staff from the molecular microbiology department was the first to be involved. Later, additional technicians had to reinforce the team and a large proportion of laboratory technicians were involved in handling SARS-CoV-2 samples. At the time of the study, 9,727 samples had been processed in the laboratory, among which 3,182 were positive for SARS-CoV-2 (32.7%).

In April 2020, a screening campaign was proposed to the whole laboratory staff of the Nancy University Hospital to determine their anti–SARS-CoV-2 serological status. All eligible laboratory workers were asked to complete a questionnaire. The following clinical and epidemiological data were collected: year of birth, sex, department within the laboratory (ie, hematology, microbiology, reproductive biology, human leukocyte antigen typing, immunology, molecular microbiology, cytometry, emergency analyses, reception and dispatching, automated analyses, genetic, pharmacology, biochemistry, point-of-care supervision, information technology support, management, environmental biology, biopathology, cleaning, and hemophilia center), and exposure to sample triple packaging or to respiratory and stool samples, exposure to a confirmed or suspected COVID-19 case (in a professional or personal context). Data regarding COVID-19–linked symptoms (ie, flu-like syndrome, dry cough, digestive disorders, loss of taste and smell) were also collected.

The detection of anti–SARS-CoV-2 IgM and IgG was performed using a flow lateral immunoassay (Biosynex BSS IgM/IgG, Biosynex Swiss Illkirch-Graffenstaden, France). Staff with positive serology and without a prior COVID-19 diagnosis were recommended for RT-PCR in nasopharyngeal swab and further serological follow-up.

The association between exposure to sample triple packaging, exposure to respiratory or stool samples collected to detect SARS-CoV-2, symptoms attributable to COVID-19, and SARS-CoV-2 seroprevalence were tested using the χ ^{Reference Kasztelewicz, Janiszewska, Burzyńska, Szydłowska, Migdał and Dzierżanowska-Fangrat2} test or the Fisher exact test, according to condition of use. P values were two-tailed, and the significance level was set at .05. We used SAS version 9.4 statistical software (SAS Institute, Cary, NC) to conduct the analyses.

Among 417 laboratory workers, 396 were eligible for the study. Most workers were women (81.1%). The median age was 42.5 years (range, 20–68). In total, 178 laboratory workers (44.9%) had been in contact with COVID-19 samples packaging, while 147 (37.1%) had been in contact with stool and/or respiratory samples (Table 1). For the management of the pandemic, 35 (8.8%) laboratory workers were specifically involved in the COVID-19 diagnosis sector. Overall, 135 (34.1%) and 109 (27.5%) workers had been in contact with a confirmed or suspected COVID-19 case, respectively.

SARS-CoV-2 antibodies were detected in 9 laboratory workers (seroprevalence, 2.3%). The most exposed persons were maintenance agents, microbiology technicians, and COVID-19 area staff, but the laboratory department was not associated with SARS-CoV-2 seroprevalence (P = .54). Likewise, handling COVID-19 sample packaging (P = .74) or handling samples from confirmed or suspected COVID-19 patients (P = .30) were not associated with SARS-CoV-2 seroprevalence.

The laboratory workers had a median age of 42.5 years (range, 20–68), and most were women. A large study on HCWs did not show any association between age or sex with positivity for SARS-CoV-2 IgG. ^{Reference Kasztelewicz, Janiszewska, Burzyńska, Szydłowska, Migdał and Dzierżanowska-Fangrat2} Interestingly, sex differences were observed in the perception of epidemic, with women being more emotionally affected and giving more attention to protective measures. ^{Reference Huang, Luo, Wang, Jin and Zeng3}

Many studies have evaluated SARS-CoV-2 seroprevalence in the general population and hospital HCWs, but to our knowledge, no studies have focused on laboratory staff. In HCWs, the seroprevalence was higher, reaching 8.5% in Geneva University Hospital employees ^{Reference Martischang, Iten and Arm4} and 13.35% in a COVID-19–dedicated hospital in India. ^{Reference Mahto, Banerjee, Biswas, Kumar, Agarwal and Singh5} In these studies, the proportion of anti–SARS-CoV-2 seroconversion was higher in employees working in COVID-19 areas. Risk factors included nosocomial outbreak and the use of public transportation. ^{Reference Martischang, Iten and Arm4} This last point was not evaluated in our study, but other nonprofessional risk factors, such as a contact with COVID-19 confirmed case, were not associated with a seroconversion.

In the urban area of the hospital around the same date, the raw SARS-CoV-2 seroprevalence was 2.1% among 2,006 individuals, ^{Reference Gégout Petit, Jeulin and Legrand6} suggesting the absence of high risk among laboratory staff, probably due to the strict application of the recommendations of the French Society of Microbiology (SFM) concerning sample handling. The benefit of correct use of personal protective equipment was also observed in HCWs, even in the most exposed groups. ^{Reference Caselli, Loconsole, Dario, Chironna and Aricò7}

Despite the small size of the cohort and of self-reporting data collection, the work presented here originally targets SARS-CoV-2–exposed laboratory staff. Today, most staff have been vaccinated, and studies evaluating the exposure of laboratory workers to a new airborne and/or hand-borne pathogen will no longer be possible. These data confirm the effectiveness of the good laboratory practices, which have to be quickly applied in future viral emergencies.

Table 1. Characteristics of the Laboratory Staff Cohort

Note. RT-PCR, reverse-transcription polymerase chain reaction.