Seroprevalence of COVID-19 IgG antibodies among healthcare workers of Pakistan: a cross-sectional study assessing exposure to COVID-19 and identification of high-risk subgroups.

OBJECTIVE: In this study, we aimed to find the seroprevalence of healthcare workers (HCWs) of Pakistan involved in the treatment and care of patients with COVID-19. SETTING: This was a cross-sectional study and total of 15 000 HCWs involved in providing services and care to the patients with COVID-19 were randomly selected from all over Pakistan. PARTICIPANTS: Informed consent was taken from all participants and were included according to inclusion and exclusion criteria. All testing was done on serum samples for the qualitative detection of SARS-CoV-2 IgG antibodies using Abbott Chemiluminescent microparticle immunoassay. An index of 1.4 was used as a cut-off to mark reactive and non-reactive cases. SPSS V.23.0 was used for data analysis. OUTCOME: Immune status of the study population depicting seroprevalence among HCWs. RESULTS: Out of all the candidates, majority of the HCWs were men (61.9%) and were doctors (62.4%). The mean age of participants was 32.8 years (SD 8.7) and majority were asymptomatic (51.8%). In this study, 33% of the HCWs were reactive for SARS-CoV-2 IgG antibody. Around 44% of the reactive cases were asymptomatic. The symptoms more significantly associated with seropositivity were: fever (OR 1.31; 95% CI 1.16 to 1.48), headache (OR 2.43; 95% CI 2.16 to 2.73), cough and shortness of breath (OR 2.10; 95% CI 1.91 to 2.31), loss of sense of smell or taste (OR 3.70; 95% CI 3.29 to 4.17) (p<0.001). Factors which showed significant association with the presence of antibodies were professional category (absolute risk (AR) 0.09; OR 1.46; 95% CI 1.36 to 1.56), availability of protective masks (AR 0.02; OR 0.90; 95% CI 0.84 to 0.96), safety goggles (AR 0.02; OR 0.90; 95% CI 0.84 to 0.97) and living arrangements (AR 0.03; OR 1.12; 95% CI 1.04 to 1.20) (p<0.05). CONCLUSION: Our study showed a high seropositivity of HCWs dealing with patients with COVID-19 in Pakistan revealing significant association with professional category, nature of work place and precautions taken while performing duties.

Seroconversion in Newly Diagnosed Cases of Coronavirus Disease.

OBJECTIVE: To determine the percentage of seroconverted real time reverse transcriptase polymerase chain reaction (RT-PCR) positive coronavirus disease (COVID-19) cases at different days post-symptom onset; and also find the agreement of chemiluminescence assay used for total antibody detection using RT-PCR as a reference method. STUDY DESIGN: Cross-sectional study. PLACE AND DURATION OF STUDY: Chughtai Institute of Pathology from April to May 2020. METHODOLOGY: Fifty pre-pandemic samples (healthy population) and 75 COVID-19 patients were included in the study. RT-PCR confirmed COVID-19 patients were divided into 3 equal groups (25 each), according to the days of symptom onset. The samples were analysed using electro-chemiluminescence as assay principle. Positive and negative agreement of COVID-19 antibodies was calculated using EP evaluator to find out the sensitivity of chemiluminescence assay for total antibody detection. The results were analysed using SPSS version 23.0. RESULTS: All the pre-pandemic samples tested were negative for antibodies with a negative agreement of 100%. Total agreement at day 7 post-symptom onset was 84%; whereas, it was 94% at day 14 and increased rapidly to 100% at day 21 post-symptom onset. At day 7 post-symptom onset, 68% of patients were seroconverted; and this percentage was 88% and 100% at day 14 and 21 post-symptom onset, respectively. CONCLUSION: Pre-pandemic samples were non-reactive for COVID-19 antibodies and seroconversion started within the first week post-virus exposure. There was 100% concordance between RT-PCR result and antibody positivity 21 days post-symptom onset. Key Words: COVID-19, SARS CoV-2, Seroconversion, Chemiluminescence.

Thermoelectric Properties of n-Type Molybdenum Disulfide (MoS2) Thin Film by Using a Simple Measurement Method.

In this paper, a micrometre thin film of molybdenum disulfide (MoS2) is characterized for thermoelectric properties. The sample was prepared through mechanical exfoliation of a molybdenite crystal. The Seebeck coefficient measurement was performed by generating a temperature gradient across the sample and recording the induced electrical voltage, and for this purpose a simple measurement setup was developed. In the measurement, platinum was utilized as reference material in the electrodes. The Seebeck value of MoS2 was estimated to be approximately -600 µV/K at a temperature difference of 40 °C. The negative sign indicates that the polarity of the material is n-type. For measurement of the thermal conductivity, the sample was sandwiched between the heat source and the heat sink, and a steady-state power of 1.42 W was provided while monitoring the temperature difference across the sample. Based on Fourier's law of conduction, the thermal conductivity of the sample was estimated to be approximately 0.26 Wm-1 K-. The electrical resistivity was estimated to be 29 Ω cm. The figure of merit of MoS2 was estimated to be 1.99 × 10-4.