Updates

By Carol A. Kemper, MD, FACP, Clinical Associate Professor of Medicine, Stanford University, Division of Infectious Diseases; Santa Clara Valley Medical Center, Section Editor: Updates; is Associate Editor for Infectious Disease Alert.

Vertical HIV Transmission in the United States

Source: MMWR. Enhanced perinatal surveillance — 15 areas, 2005-2008. Available at: www.cdc.gov/hiv/surveillance/resources/reports/2010supp_vol16no2/index.htm.

The United States Perinatal HIV Surveillance Project tracks HIV-infected pregnant women in care in 15 locations throughout the United States and Puerto Rico. Data for the period of 2005-2008 provides insight into the epidemic's effects on HIV+ women, and the risk of maternal-child HIV transmission. During this 4-year period, data for 8,054 mother-baby pairs were collected. About half (54%) of the identified pregnant woman with HIV infection were U.S.-born, one-third were unknown, and the remainder were from a variety of other countries, generally in Central America and Africa. Six percent were < age 20, 21% were age 20-24, 49% were age 25-34, and 24% were ≥ age 35 at the time of delivery.

From 2005 to 2008, the majority of HIV+ pregnant women were African-American (65%) or Latina (23%). Nearly half were heterosexually exposed to HIV. At the time of delivery, 55% were unmarried, 15% were married, and the marital status of 28% was unknown.

Two-thirds of the women were aware of their HIV status at the time of their pregnancy; only a minority learned of their positive HIV status during pregnancy screening (26%) or at the time of delivery (3%). Of those whose HIV status was recognized before their pregnancy, 84% were in care and on antiretroviral therapy (ART). During pregnancy, 90% of HIV+ women were receiving perinatal care (7% were not and 3% were unknown) and 85% were receiving ART.

A total of 179 infants (2%) were confirmed HIV+; a significant number of infants (27%) were either lost to follow-up, or the results of the HIV tests were pending or indeterminate (as of December 2009). Only 71% were known to be HIV-negative. These figures were similar regardless of ethnicity. The number of birth defects was lowest for Asians (2%) and highest for African Americans (6%) and Latinos (7%).

Screening of pregnant woman for HIV remains a priority for every Ob-Gyn and pregnancy clinic, regardless of perceived risk for HIV. More than half of the women in this survey had no identifiable risk factor other than a sexual partner, which is pretty much true for every pregnant woman. Identifying these women early in their pregnancy and getting them on ART is essential to preventing maternal-child HIV transmission. The French Perinatal Cohort Study, a comparable program in France, recently published data on 7,425 mother-infant pairs.1 The overall rate of HIV transmission to infants was 1.5% — somewhat better than the U.S. data. And the rate of mother-baby HIV transmission for women who were virologically suppressed at the time of delivery (< 20 copies per mL) was only 0.4%. If the United States could come close to achieving these results, more than 100 children in this study could have been successfully protected from HIV infection.

Reference

  1. Tubiana R, et al. Factors associated with mother-to-child transmission of HIV-1 despite a maternal viral load < 500 copies/mL at delivery: A case-control study nested in the French Perinatal Cohort (EPF-ANRS C01). Clin Infect Dis 2010;50:585-596.

The Appendix as Protector

Source: Im GY, et al. The appendix may protect against Clostridium difficile recurrence. Clin Gastroenterol Hepatol 2011 June 13; Epub ahead of print.

Although the appendix has been much maligned as a vestigial organ of uncertain value, these authors theorized that the lymphoid tissue and biofilm produced by the intact appendix may protect against intestinal infection with Clostridium difficile (CDI). They examined the medical records of 396 patients admitted to a tertiary care center between January 2005 and January 2007 with a diagnosis of CDI. A total of 254 patients with CDI and known appendix status were included in the analysis (76% with a first episode of CDI and 24% with a recurrent episode of CDI). The median age of the group was 79 years. The rate of colectomy was 2.5% and mortality was 5.6%.

Multivariate analysis of 11 different variables suggested that patients older than 60 years were at greatest risk for relapse (P = 0.028, adjusted relative risk [ARR] 2.44). In addition, the presence of an appendix appeared to be highly protective of CDI relapse (P < 0.0001, ARR 0.398). The CDI recurrence rate was 45% for those without an appendix and only 18% for those with an appendix. Further study is needed to confirm these results prospectively.

Tdap for Health Care Workers

Source: ACIP Provisional recommendations for health care personnel on use of tetanus toxoid, reduced diptheria toxoid, and acellular pertussis vaccine (Tdap) and use of post-exposure anitmicrobial prophylaxis. Available at: www.cdc.gov/vaccines/recs/provisional/default/htm.

Add Tdap to the growing list of recommended (and often required) vaccinations for health care workers (HCWs) in hospital, including MMR, hepatitis B, influenza, and possibly varicella. In April, the American College of Immunization Practices (ACIP) issued provisional recommendations for pertussis vaccination (Tdap) of all hospital HCWs, regardless of age and prior vaccine history (i.e., regardless of the time since last Td dose). Current hospital employees (and future hires) should receive a single dose of vaccine now, in one broad sweep to provide blanketed coverage of every hospital, and then continue to receive the usual booster vaccine recommended for adults.

Pertussis appears to be cycling up in our communities, especially in California, where 8,383 cases were reported in 2010, including 10 deaths in infants. Neonates and infants < 12 months of age are at the greatest risk for severe infection. For this reason, initial ACIP recommendations were to provide vaccination to all caregivers of small children, thus providing a protective "cocoon" of immunogenic individuals. The current recommendations expand on this philosophy, especially to physicians and nurses who provide care for infants and small children.

HCWs are at risk for pertussis exposure — both from their patients and fellow colleagues. Outbreaks of pertussis in the hospital setting can rapidly evolve, resulting in significant hours and effort to provide post-exposure prophylaxis to everyone exposed. Those who develop symptoms of pertussis are required to receive antibacterial therapy and are furloughed for a minimum of 5 days. In two separate outbreaks in Minnesota, 12% and 52% of cases occurred in HCWs who were exposed to either an ill index case or to each other. At our county hospital in the 1990s, an outbreak of a pertussis-like illness (pre-PCR test availability) necessitated the administration of chemoprophylaxis to more than 400 HCWs; a supreme effort over a Memorial day weekend, with significant cost to the hospital.1

HCWs who have received Tdap vaccine nonetheless require close monitoring for signs and symptoms for 21 days after pertussis exposure. Post-exposure prophylaxis is still recommended for vaccinated HCWs with documented exposure. Even mild respiratory symptoms (e.g., runny nose, sneezing, low grade fever, or cough) should prompt PCR testing for pertussis, receipt of antibiotics, and furlough from work for 5 days. The paroxysmal stage of pertussis, with the characteristic cough, generally only begins 1-2 weeks into the illness.

Reference

  1. Martinez SM, et al. Azithromycin pro-phylaxis during a hospitalwide outbreak of a pertussis-like illness. Infect Control Hosp Epidemiol 2001;22:781-783.

The Buzz on TB

Source: Suckling DM, Sagar RL. Honeybees Apis mellifera can detect the scent of Mycobacterium tuberculosis. Tuberculosis 201191:327-328.

First there were lab techs, peering through microscopes to identify acid-fast organisms, and then there were Gambian rats, who could sniff out tuberculosis (MTb), like small incendiary devices in sputa. Now, there are trained honeybees...

Recent work has focused on the aromatic compounds characteristic to MTb that allow Gambian rats to "sniff out" the organism in sputa, and may allow other more sensitive means for identification of active pulmonary tuberculosis infection. Three such compounds have been identified, which are considered aromatic "signatures" of both Mycobacterium tuberculosis and M. bovis. The compounds include methyl phenylacetate, methyl-p-anisate, and methyl nicotinate.

These authors cleverly manipulated honeybees to recognize these compounds using their proboscis extension reflex. Once "trained," 20-25 honeybees were exposed to filter paper inoculated with one of the three compounds in varying amounts, blown with small puffs of air, alternating with clean air every 10 seconds. The number of bees exhibiting a response to the presence of varying dilutions of each of the compounds compared with a neutral control was determined. Methyl-p-anisate provided the best response, followed by methyl phenylacetate (which has a jasmine-like odor), with as little as 10 picograms eliciting a response. Response to methyl nicotinate was less robust, and required a threshold concentration of 1 ng. The honeybees were able to detect these compounds over 8 orders of magnitude!

So, how do you train a honeybee? First, you collect some fresh foragers from the garden in the late afternoon... Then you chill them to -4° C for 2 minutes, insert them in a plastic tube, so only their head and tongue can move, then feed them a 50% sucrose solution till they are full. Then starve them overnight at 28° C, careful to keep them warmer when not eating. In the morning, chill them down to 23° C for 10 minutes, and then begin the conditioning. Every time they correctly elicit a proboscis extension reflex to one of the signature compounds, reward them with sugar solution for 5 seconds. Those bees that fail training are given a pink slip. They were probably not great foragers anyway.