Diagnostic performance of COVID-19 serology assays.

INTRODUCTION: The World Health Organization (WHO) declared COVID-19 outbreak as a world pandemic on 12th March 2020. Diagnosis of suspected cases is confirmed by nucleic acid assays with real-time PCR, using respiratory samples. Serology tests are comparatively easier to perform, but their utility may be limited by the performance and the fact that antibodies appear later during the disease course. We aimed to describe the performance data on serological assays for COVID-19. MATERIALS AND METHODS: A review of multiple reports and kit inserts on the diagnostic performance of rapid tests from various manufacturers that are commercially available were performed. Only preliminary data are available currently. RESULTS: From a total of nine rapid detection test (RDT) kits, three kits offer total antibody detection, while six kits offer combination SARS-CoV-2 IgM and IgG detection in two separate test lines. All kits are based on colloidal gold-labeled immunochromatography principle and one-step method with results obtained within 15 minutes, using whole blood, serum or plasma samples. The sensitivity for both IgM and IgG tests ranges between 72.7% and 100%, while specificity ranges between 98.7% to 100%. Two immunochromatography using nasopharyngeal or throat swab for detection of COVID-19 specific antigen are also reviewed. CONCLUSIONS: There is much to determine regarding the value of serological testing in COVID-19 diagnosis and monitoring. More comprehensive evaluations of their performance are rapidly underway. The use of serology methods requires appropriate interpretations of the results and understanding the strengths and limitations of such tests.

Hepatitis B seroepidemiology and booster vaccination in pre-clinical medical students in a Malaysian university.

INTRODUCTION: Infant hepatitis B vaccination was introduced into the Expanded Programme on Immunisation (EPI) in Malaysia in 1989. This study aimed to investigate seroprevalence of hepatitis B among UKM pre-clinical medical students, born between 1991 and 1995, and had their infant vaccination more than 20 years ago. MATERIALS AND METHODS: A prospective, cross-sectional study involving 352 students, comprising 109 (31.0%) males and 243 (69.0%) females. Blood specimens were tested for anti-HBs, where levels of ≥10 mIU/mL was considered reactive and protective. Students with non-reactive levels were given a 20 µg HBV vaccine booster. Anti-HBs levels were tested six weeks after the first booster dose. Those with anti-HBs <10 mIU/mL were then given another two booster doses, at least one month apart. Anti-HBs levels were tested six weeks after the third dose. RESULTS: Ninety-seven students (27.6%) had anti-HBs ranging from 10 to >1000 mIU/mL while 255 (72.4%) had anti-HBs <10 mIU/mL. After one booster dose, 208 (59.1%) mounted anti-HBs ≥10 mIU/mL. Among the remaining 47 (13.3%), all except two students (0.6%) responded following completion of three vaccination doses. They were negative for HBsAg and anti-HBcore antibody, thus regarded as non-responders. CONCLUSIONS: Anti-HBs levels waned after 20 years post-vaccination, where more than 70% were within non-reactive levels. For healthcare workers, a booster dose followed by documenting anti-HBs levels of ≥10 mIU/mL may be recommended, to guide the management of post-exposure prophylaxis. Pre-booster anti-HBs testing may not be indicated. Serological surveillance is important in long-term assessment of HBV vaccination programs. No HBV carrier was detected.

Evaluation of IgM LAT and IgM ELISA as compared to microscopic agglutination test (MAT) for early diagnosis of Leptospira sp.

Leptospirosis is a worldwide zoonotic disease caused by spirochetes of the genus Leptospira. The clinical manifestation of leptospirosis is non-specific and frequently misdiagnosed as other illnesses. The aim of this study was to compare the diagnostic accuracies of two commercial tests for early diagnosis of Leptospira species: the IgM latex agglutination test (IgM LAT) and the IgM enzyme-linked immunosorbent assay (IgM ELISA). A total of 140 serum samples were obtained from patients suspected of leptospirosis at the Universiti Kebangsaan Malaysia Medical Centre (UKMMC). These serum samples were tested for the presence of Leptospira sp. using IgM LAT, IgM ELISA and MAT. From Table 1, IgM LAT showed 21% (n = 29) positive, 18% (n = 25) inconclusive and 61% (n = 86) negative, while IgM ELISA showed 6% (n = 8) positive, 6% (n = 8) inconclusive, 88% (n = 124) negative and MAT showed 11% (n = 16) positive, 47% (n = 65) inconclusive, 42% (n = 59) negative. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of IgM LAT were 68.8%, 57.6%, 30.6% and 87.2% respectively, while for IgM ELISA they were 37.5%, 89.8%, 50% and 84.1%, respectively as compared to MAT (Table 2). The results showed that IgM LAT had higher sensitivity but lower specificity compared to IgM ELISA. In conclusion, IgM LAT can be useful as an early screening test for early diagnosis of Leptospira sp., while IgM ELISA is a suitable method for reducing false negative detection of Leptospira sp. As both tests show moderate percentages (~65%) in accuracy, an additional test is required for better detection of Leptospira sp.