Snapshots for May 2004 (2004)

HIV TESTING IN PREGNANT WOMEN The availability of antiretroviral drugs to prevent maternal-fetal transmission of HIV and to treat the pregnant woman herself has led to heightened interest in prenatal testing.1 Although unpublished data from the Centers for Disease Control and Prevention show that most women (93% in a 25-state survey) know their HIV status before delivery, 280 to 370 transmissions continue to occur each year. US states and Canadian provinces have tried 3 strategies for testing. The "opt-in" approach provides women with pretest counseling and requires specific consent. In the "opt-out" approach, women are told that an HIV test will be included in the routine battery, but they may refuse the test. The "mandatory newborn testing" approach tests all newborns for HIV unless the mother's status is known. Using a complex data collection scheme from several data sources, the opt-in approach was found to yield testing rates in the range of 25% to 83% (most values in the 60% range), the opt-out approach yielded rates of 85% (Tennessee) to 98% (Canada), and the mandatory newborn testing approach yielded rates of 52% (areas without expedited testing) to 83% (results returned within 48 hours). The preferred strategies are the opt-out or, with expedited results, mandatory newborn testing. ARE METHICILLIN-RESISTANT STRAINS OF STAPHYLOCOCCUS AUREUS MORE VIRULENT? There has long been a debate about the relative virulence of antibiotic-resistant strains compared with susceptible strains of the same species. Cosgrove et al2 carried out a meta-analysis of the mortality associated with Staphylococcus aureus bacteremia in studies published between 1980 and 2000. All of the studies were retrospective. Thirty-one studies were deemed suitable for data extraction. Of about 2600 patients in these reports, 2/3 of them had bacteremia due to methicillin-susceptible S. aureus (MSSA), and the rest had infection by methicillin-resistant strains (MRSA). Seventy-seven percent of the 31 individual studies showed no significant difference in mortality of bacteremia between MRSA and MSSA strains. However, combining the results of all studies, the pooled odds ratio for death was 1.93 (95% confidence intervals 1.54 to 2.42) with MRSA compared with MSSA strains infections. There was marked heterogeneity among the studies. However, analysis of subsets comparing nosocomial versus community acquisition of the infection, outbreaks as opposed to endemic infections, central line infections and endocarditis, and mortality specifically related to the infection as opposed to all-cause mortality all yielded odds ratios in the range of 1.5 to 2.0, with most being statistically significant. The authors attribute the failure of individual studies to detect a higher mortality with MRSA infections to the small size of those studies. Possible reasons for a worse outcome with MRSA strains could be that (1) those strains are more virulent (a hypothesis for which there is no evidence), (2) a lesser efficacy of vancomycin against MRSA than of antistaphylococcal β-lactams against MSSA strains (a theory for which there is some evidence), and (3) failure to administer vancomycin in timely fashion to patients with MRSA infections (a possibility that could not be directly evaluated in this meta-analysis). UNRECOGNIZED FETAL DEATH FROM PARVOVIRUS B19 INFECTION IN LATER PREGNANCY Parvovirus B19 infections are well recognized to cause intrauterine fetal death when they occur in the first or second trimester; most such pregnancies have a characteristic syndrome of fetal hydrops. Norbeck et al3 have now adduced evidence that a substantial number of intrauterine fetal death that occur in later pregnancy is attributable to unidentified infection by the virus. Among 92 women who sustained intrauterine fetal death after gestational week 22, they found Parvovirus B19 DNA by polymerase chain reaction in 13 (14%). Only 2 of the cases were hydropic, and both of these occurred in the earlier period of gestation. They conclude that Parvovirus plays a role in otherwise unexplained late gestational intrauterine fetal deaths.