Rapid detection of varicella-zoster viral antibodies by latex agglutination assay: a practical experience for medical and science undergraduates

Abstract

From 1993 to 1997, laboratory exercises have been conducted using a latex agglutination assay to detect antibodies to varicella-zoster virus (VZV) among 576 medical and science undergraduates aged 18–25 years. Of 295 students who volunteered a past history of chickenpox, there was good correlation with VZV antibody positivity (89.8%). However, despite a history of chickenpox, 30 (10.2%) tested negative for VZV antibodies, suggesting previous misdiagnosis or false negatives caused by the prozoning phenomenon due to unusually high VZV antibody levels. Indeed, out of 22 initially seronegative sera from selected students with a history of chickenpox, 13 sera were subsequently seropositive upon re-testing the sera at higher dilutions. Although 192 students gave a negative history of chickenpox, 22 (11.5%) tested positive for VZV antibodies (of whom 2 were vaccinated, with the rest reflecting previous subclinical infection). Of 89 subjects unsure of their history of chickenpox, 30 (33.7%) were seropositive. Thus elicitation of a history of symptoms of chickenpox may not be a reliable indicator of past VZV exposure. While 55% of this cohort of this cohort of young adults were seropositive, a significant fraction of seronegative individuals (45%) were still susceptible to VZV infection. This practical study exemplifies latex agglutination as a rapid and simple diagnostic technique, and integrates certain key principles of virology, immunology and medicine.