Background:  GB virus C (GBV-C) viremia is associated with improved survival, non-progression, and response to ART in HIV-infected persons. We performed a matched case-control study of 133 cases of HIV-infected pregnant women who vertically transmitted HIV to their infants and 266 non-transmitting controls in the Women and Infants Transmission Study (WITS).

Methods:  Infant HIV-infection status was defined by CDC guidelines. Controls were pair-matched for high risk delivery, race and enrollment year. Frozen plasma samples from visits at or within 3 months of delivery were tested for GBV-C viremia by real-time polymerase chain reaction (RT-PCR) and E2 antibodies by ELISA. Active GBV-C infection was defined as positive GBV-C RNA and past GBV-C infection as positive GBV-C antibodies. Multivariable analyses included variables previously associated with HIV transmission risk in Women and Infant Transmission Study (WITS). Analysis was by methods of Breslow and Day for 1:2 matched data. Odds ratios (OR) with estimated 95% confidence intervals and p values were calculated.

Results:  Of 397 samples analyzed, 43 (11%) showed active GBV-C while 141 (36%) indicated past infection. An insignificant trend toward decreased mother-to-child HIV transmission (MTCT) was noted in women with active GBV-C infection (OR = 0.79, p = 0.26), but not in women with past GBV-C infection (OR = 1.00, p = 0.98). Among women delivering in the HAART era (since August 1996) GBV-C viremia was associated with reduced MTCT (OR = 0.30, p = 0.06), but no effect was seen in women delivering in the pre-HAART era (1989 until July 1996). Of variables historically associated with increased MTCT in WITS, low birth weight, lack of HAART therapy, and maternal HIV RNA copy number during pregnancy still remained associated in this study. GBV-C viremic women had lower HIV RNA copy numbers and higher CD4 counts (p = 0.01 and 0.0006, respectively), and were more likely to have HIV RNA <1000 copies/mL than women without GBV-C infection (28.6% vs 15.6%). Of 44 women with HIV RNA >100,000 copies/mL at delivery, none was positive for GBV-C RNA.

Conclusions:  GBV-C viremia was associated with lower HIV viral load and higher CD4 counts in pregnant women, perhaps explaining its association with decreased MTCT in some other studies. The protective impact of GBV-C viremia during the HAART era is consistent with other studies that show an enhanced response to HAART in GBV-C co-infected patients. Further studies with larger or multiple cohorts are necessary to assess possible benefit in terms of MTCT.