The detection of varicella zoster antibodies by simultaneous competitive EIA and its comparison with radioimmunoassay, latex agglutination and antiglobulin type EIA

Study of susceptibility towards varicella by screening for the presence of IgG antibodies among nursing and medical students of a tertiary care teaching hospital in pune, India

BACKGROUND

It is believed that all suffer from chickenpox infection in their childhood. Many studies abroad and some in India clearly indicate that many individuals escape the infection in childhood, and thus, remain susceptible in adulthood. Adulthood chickenpox is a more serious infection than childhood. Prior screening of health care workers for the presence of IgG antibodies against Varicella will not only prevent hospital outbreaks but also economic and academic loss faced by the students. This will also have an important implication in terms of patient care as there is a threat of spreading Varicella to immuno-compromised patients. Definite history of prior infection of chickenpox is considered as an indicator for immunity towards the same. However, the reliability of this needs to be tested.

AIM

A study to assess the susceptibility of nursing and medical students towards Varicella infection by screening for IgG antibodies against Varicella virus and to identify any risk factors for the same.

SETTINGS AND DESIGN

A hospital-based cross-sectional study in nursing and medical students.

MATERIALS AND METHODS

Total 78 nursing and medical students participated in the study. They were given prestructured and pretested questionnaires. After obtaining informed consent, blood sample was collected and screened for the presence of IgG antibodies against Varicella by Enzyme Linked Immunosorbent Assay (ELISA) by using a commercial kit.

STATISTICAL ANALYSIS

Epi_info 2002 was used for analysis. Age of the study subjects were summarized as mean age and standard deviation. Susceptibility was analyzed as percentage with 95% confidence interval and Chi Square test was used to find association of susceptibility status with sex and region of residence in childhood. Relevance of definite history as an indicator for immunity was assessed by calculating sensitivity, specificity, positive and negative predictive values with 95% confidence interval.

RESULTS

Twenty males (25.6%) and 58 females (74.4%) participated in the study from medical and nursing students. The mean age ± standard deviation of mean was 19.4 ± 1.42 years for female students and 20.8 ± 2.13 years for male students. Total 20 (25.6%) students were found to be susceptible to Varicella with the confidence interval ranging from 15.8% to 35.4%. With respect to the gender of the students, the difference between the susceptibility percentage in female students (32%) and in male students (14.3%) was only a numerical difference and not statistically significant (χ(2) = 2.098, P=0.147, d.f. = 2). Also, the susceptibility was seen significantly more among Keralite students (Pearson Chi-Square=16.736, d.f=6, P=0.008; Likelihood Ratio=15.086, d.f=6, P=0.035; Fisher's Exact Test=13.569, p=0.022). The sensitivity of definite history of prior chickenpox infection as an indicator of immunity was only 55.17%, with C.I ranging from 43.9% to 66.4%, specificity was 80%, with C.I. ranging from 70.9% to 86%, and positive predictive value was 88.8% with C.I of 81.7% to 89% and negative predictive value of history of 66.6% with C.I. of 56% to 77.2%.

CONCLUSION

Total 20 (25.6%) students were found to be susceptible to Varicella with the confidence interval ranging from 15.8% to 35.4%. Thus, there is a need for vaccination of all susceptible individuals. Definite history of prior chickenpox infection is not a reliable indicator of immunity against the same. The investigators recommend screening for IgG antibodies against Varicella of all students selected for the M.B.B.S. (Bachelor of Medicine and Bachelor of Surgery) and nursing course, and vaccination for susceptible individuals to prevent institutional outbreak and academic loss.

Serum concentrations, efficacy, and safety of a new, intravenously administered varicella zoster immune globulin in pregnant women

Chickenpox is teratogenic in humans, and varicella zoster immune globulin (VZIG) is given to pregnant women believed to be susceptible to the virus after contact with chickenpox. Available VZIG is given as intramuscular injections. The objective of this study was to evaluate the efficacy, safety, and serum concentrations of a new VZIG that can be given intravenously. The new VZIG (Cangene Pharm., Inc.) was compared to the standard VZIG (Massachusetts Public Health Biologic Laboratories) in a randomized protocol in 57 pregnant women seronegative to varicella zoster virus (VZV). Pregnant women received 125 units per 10 kg body weight to a maximal dose of 625 units. Women were evaluated on days 2, 7, 14, and 28 and at other times if symptoms developed into clinical varicella, which was scored by the Constitutional Illness Score. The new VZIG was comparable to the standard VZIG on all parameters of efficacy and safety. Levels of VZV antibodies at day 2 postinjection were significantly higher among those receiving the new preparation intravenously. The authors concluded that the new intravenous form of VZIG confers higher initial levels of VZV antibodies and is comparable in terms of its maternal efficacy and safety to the standard form of VZIG.

Assays for antibodies to varicella-zoster virus

Anti-varicella-zoster virus serum antibody assays and their use in vaccine development are described. Of particular interest are FAMA and neutralization assays and the gpELISA. These and other assays are compared and summarized in terms of characteristics including biologic relevance, sensitivity, specificity, and suitability for different laboratory and clinical applications.

Determination of varicella-zoster virus (VZV) immune status with the VIDAS VZV immunoglobulin G automated immunoassay and the VZVScan latex agglutination assay

The VIDAS varicella-zoster virus (VZV) immunoglobulin G immunoassay and the VZVScan latex agglutination (LA) test were compared for the detection of VZV antibody in patient sera. Of 625 samples tested, 554 were positive for VZV antibody by one or both methods. Five hundred thirteen (82.1%) samples were positive by both methods, 71 (11.4%) were negative by both methods, and there were 41 (6.6%) discrepant samples. Statistically significant differences in sensitivity and specificity were not found (P = 0.37); however, several observations were made. All 23 VIDAS repeat equivocal samples were LA positive. Fifty-four samples showed prozone effects with the LA assay, all of which resolved as positive.