Varicella zoster Virus IgG Antibody Levels in HIV Infected Patients Managed at Ryan White Clinics in Three South Carolina Counties
Authors: Julio C. Arroyo, MD, Hope-Health Ryan White Clin, Florence, SC and Timothy Hanson, PhD, Univ. of South Carolina, Columbia, SC
Background: Infections due to Varicella zoster virus (VZV) are common in HIV infected patients (HIVP), yet antibody levels to VZV are not routinely measured. To better understand host-VZV dynamics in HIVP plus assess the clinical utility of a commercial assay, IgG levels were measured and correlated with CD4 count, viral load (VL), history (HX) of Herpes zoster (HZ) and demographics.
Methods: Specimens were processed using a semi-quantitative assay. Results reported as an index: <135 consistent with Òabsence of immunityÓ, 135-165 ÒequivocalÓ, and >165 reflected ÒimmunityÓ. Cutoff point reported as >4000. Statistical computations were performed in the R computing package (R Core Team 2017). Proportions compared using the exact chi-squared test. Highly skewed variables compared using the Mann-Whitney-Wilcoxon test, and censored variables compared via a generalization of MWW (log-rank).
Results: During 22 months, 426 HIVP enrolled, 284 (66%) males and 142 females; mean age was 44 and 51, respectively. Mean IgG index for all HIVP =1886, males=1971, females=1720 (p=0.06). However, difference in median IgG was significant (1730 vs 1477; p<0.0001). Hx of HZ was elicited in 113 (27%), no gender difference (27% vs 25%, p=0.55). Frequency of IgG>4000 was not significant. HIVP subdivided into 3 age groups for further comparisons. Age<=30: 79 HIVP, 87% of which were males, only 9 (11%) had Hx of HZ, lowest mean IgG=1686 and least HIV control. VL<50 c/ml in 44%. Age 31 to 59: 274 HIVP with mean age of 47, mean IgG=1908, and 72% with VL<50. A Hx of HZ in 86 (31%). Age=>60: 73 HIVP with mean age of 65, mean IgG=2006. Eighteen had Hx of HZ. Compared to second group, oldest group had better HIV control with VL<50 in 79% (p=0.039) yet mean IgG was similar (p=0.33). Through a logistic regression analysis, the probability of HZ steadily increased as a function of age until about 55. IgG indexes>4000 were also noted in 58 asymptomatic HIVP.
Conclusion: Intermittent, asymptomatic VZV reactivation occurs in HIVP regardless of prior HZ. IgG<135 predicted negative Hx of HZ. Pre-existing IgG may not protect against VZV reactivation.