key: cord-0750990-5j57ysl0
authors: Chau, Nguyen Van Vinh; Toan, Le Mau; Man, Dinh Nguyen Huy; Thao, Huynh Phuong; Lan, Nguyen Phu Huong; Ty, Dinh Thi Bich; Hieu, Dinh Khac; Tien, Nguyen Thi My; Ngoc, Nghiem My; Hung, Le Manh; Dung, Nguyen Thanh; Thanh, Tran Tan; Truong, Nguyen Thanh; Thwaites, Guy; Van Tan, Le
title: Absence of SARS-CoV-2 antibodies in health care workers of a tertiary referral hospital for COVID-19 in southern Vietnam
date: 2020-11-19
journal: J Infect
DOI: 10.1016/j.jinf.2020.11.018
sha: d8bf133476c1f425561eddbd6138d93ef48195b4
doc_id: 750990
cord_uid: 5j57ysl0

nan

CoV-2 in health care workers worldwide was between 1.2% -17.4% [1] [2] [3] [4] . Such knowledge is essential to assess the effectiveness of infection prevention measures and to minimize the risk of nosocomial infection.

In Vietnam, the first cases of coronavirus disease 2019 (COVID-19) were reported on 23 rd January 2020. Since then there have been two major COVID-19 epidemic waves attributable to locally acquired infection, one in March/April and the second in July/August The Hospital for Tropical Diseases (HTD) in HCMC is a 660-bed tertiary referral hospital for patient with infectious diseases in southern Vietnam (population >40 million). HTD has 700 staff and two designated centres for COVID-19 patients located in the West and the East of HCMC. These two centres and HTD main campus are run HTD members of staff, and are responsible for receiving and treating COVID-19 patients, especially those with severe infection, in southern Vietnam [6] . As a reference laboratory, HTD is also responsible for SARS-CoV-2 testing in HCMC. By the end of August 2020, nearly 50,000 SARS-CoV-2 PCRs were conducted by the HTD laboratory.

During the last week of August, we conducted a sero-survey of SARS-CoV-2 antibodies amongst the HTD staff to assess the risk of nosocomial infection. We invited any hospital staff regardless of their occupations and the nature of their work to participate in the study.

We collected demographics, occupation and information about SARS-CoV-2 exposure (caring for COVID-19 patients or conducting SARS-CoV-2 testing). For SARS-CoV-2 antibody measurement, we collected 5ml plasma from each participant. We measured antibodies against the nucleocapsid (N) protein, a main immunogen of SARS-CoV-2 using Elecsys Anti-SARS-CoV-2 assay (Roche, Germany). The reported sensitivity and specificity this assay were 97.2% and 99.8% respectively [7] . The institutional review board of HTD approved the clinical study.

Of 700 staff of HTD, 408 consented to enroll in the study (56% response rate). The study participants included all 97 staff who provided direct clinical care for COVID-19 patients, and all 34 staff whose work involved in processing respiratory samples from COVID-19 patients. The study participants aged from 20 to 60 years with a median of 32 years.

Nurses were predominant, accounting for 35.3% (144/408), followed by medical doctors (64/408, 15.7%) and cleaners (42/408, 10.3%). More details about the characteristics of the study participants are presented in Table 1 . None of the study participants had detectable antibodies against N protein.

Our study did not find evidence of SARS-CoV-2 antibodies in 408 HTD staff, including Vietnam [8, 9] .

Seasonal coronaviruses (OC43, NL63, HKU1 and 229E) are common causes of respiratory infection worldwide with seroprevalence increasing with age [10] . It is likely that past infection with these coronaviruses might have occurred in a certain proportion of the study participants. Thus the results point to the potential of non-cross-reactivity between antibodies against these seasonal coronaviruses and the N protein of SARS-CoV-2 in the study participants. The extent to which sera collected from Vietnamese people prior to the COVID-19 pandemic could react with or neutralize SARS-CoV-2 merits further research.

In summary, antibodies against N protein of SARS-CoV-2 were not detected in 408 (56%) of health care workers of a major hospital for COVID-19 in southern Vietnam. While the results are reassuring, it remains important to conduct regular sero-surveys of SARS-CoV-2 in frontline health care workers to assess the risk of nosocomial infection. Such knowledge remains important to inform the implementation of infection prevention measures in health care settings.

Large-scale, molecular and serological SARS-CoV-2 screening of healthcare workers in a 4-site public hospital in Belgium after COVID-19 outbreak

High SARS-CoV-2 antibody prevalence among healthcare workers exposed to COVID-19 patients

Risk of COVID-19 in health-care workers in Denmark: an observational cohort study. The Lancet Infectious Diseases

SARS-CoV-2-specific antibody detection in healthcare workers in Germany with direct contact to COVID-19 patients

Official page on acute respiratory infections COVID-19

The natural history and transmission potential of asymptomatic SARS-CoV-2 infection

Performance characteristics of five immunoassays for SARS-CoV-2: a head-to-head benchmark comparison. The Lancet Infectious Diseases

Lack of SARS transmission among public hospital workers

Avian influenza H5N1 and healthcare workers

Human coronavirus NL63 and 229E seroconversion in children

Table 1: Characteristics of the study participants Demography Age, y, median (range)

Note to: *including daily medical examination, performing intubation, taking swabs for follow up PCR diagnosis and facility cleaning

GT and LVT are suppoted by the Wellcome Trust of Great Britain (106680/B/14/Z and 204904/Z/16/Z, respectively). We are indebt to Ms Le Kim Thanh and the molecular diagnostic team of the Hospital for Tropical Disease for their support. We would like to thanks Roche Diagnostics in Vietnam for kindly providing the diagnostic kit.