Introduction

COVID-19 has been declared a Pandemic by World Health Organization (WHO) in March 2020 due to the rapid spread of disease outside china affecting a growing number of countries; about 218 countries have been affected worldwide including Pakistan [1]. With the start of infection in December last year in Wuhan city of China the source of infection was identified as severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) [2].

Pakistan is dealing with huge burden of disease, with the first case reported in Pakistan on 26 February 2020. By 28 November 2020, 392356 confirmed cases have been reported in Pakistan with 7942 deaths [3]. HCWs are involved in management of the cases of this infectious disease. With increased working hours and working in a potentially infectious environment is fatiguing both mentally and physically. On 25 February 2020, China reported 3387 infected HCWs in Hubei alone, at least 18 of whom died, causing growing concern among HCWs [4].

For diagnosis of infection, two methodologies are used, reverse transcription Polymerase Chain Reaction (RT-PCR) which is considered gold standard. The diagnosis of COVID-19 is based on PCR testing of severe acute respiratory distress syndrome corona virus-2 (SARS-CoV-2) in nasopharyngeal/ oropharyngeal swab specimen of symptomatic patients [5]. This PCR testing takes longer time and may underrate the disease burden; it is expensive and requires trained staff. While second technique is antibody testing [6], which are formed in the body in response to virus and are required to encounter the infectious agent; antibody testing is easy to perform, fast and less expensive. Antibodies developed against SARS-CoV-2 may be used as a screening tool to assess the prevalence of COVID-19 infection; which can be overlooked by inadequate/ unreachable PCR testing particularly among asymptomatic patients. But sensitivity of antibody tests is too low in the first week since onset of symptoms to be considered for the diagnosis, but they complement other testing in individuals presenting later, when RT-PCR tests are negative, or are not done at all. Similarly Antibody testing can have a useful role for detecting previous SARS-CoV-2 infection if performed after more than 15 days after onset of symptoms. However, the duration of antibody rises is currently not clear, and we found very little data beyond 35 days post-symptom onset [7]. Antibody tests have been developed to detect IgG only, both IgG and IgM, or total antibodies. In a review of 54 available studies, mostly from China, the accuracy of pooled results for combination IgG/IgM tests was 91% at 15 to 21 days after onset of symptoms [8].

As Fast and accurate laboratory diagnosis of active COVID-19 infection is one of the cornerstones of pandemic control. With the numerous tests available in the market, the use of correct specimen type and laboratory testing technique in exact clinical situation remains a challenge [9]. The assessment of the clinical utility of these tests in different scenarios in COVID-19 is helpful in management of COVID-19 cases and early prediction of complications [10]. Further studies in this field are required to validate assays for precise diagnosis and newer biomarkers for monitoring treatment and progression of disease. In view of above present study was carried out to determine association between PCR and antibody positivity by assessing the antibody response in PCR positive vs PCR negative COVID-19 exposed symptomatic/ asymptomatic HCWs.

Materials and Methods

A total of 102 HCW were included in this cross-sectional study after written informed consent including doctors, nurses, laboratory and janitorial staff who were working in different wards with symptomatic COVID-19 patients and their samples. We performed antibody testing to see the development of antibodies in PCR positive HCWs and also in PCR negative HCW who were exposed to SARS COV-2 while working in closed contact with the COVID 19 positive. Specimen swabs from posterior oropharyngeal wall/ nasopharynx were taken and kept in viral transport medium to perform PCR testing of SARS-CoV-2 either at onset of symptoms or at 6 weeks (42 days) after first day of duty with COVID-19 patient and blood samples were drawn to measure the corresponding serum antibody response after recovery or at completion of 6 weeks (42 days) of their first duty in COVID-19 wards. Serum COVID-19 total antibody test was performed on fully automated chemiluminescence based immunoassay analyser Roche-COBAS 6000 with FDA approved kits.8 Pharyngeal swab RT- PCR was done on CFX-96 Biorad fully automated amplifier after RNA extraction on fully automated extractor- super extract Systaaq diagnostic products.5 Serum CRP (mg/L) was measured by immunoturbidimetry in both groups at the time of PCR test [11]. Chi-square was applied between string data for PCR and antibodies. P value of <0.05 was taken as significant.