Infectious Diseases Watch

Searching for the Source as Cholera Ravages Haiti

Since October 2010, when cholera appeared in Haiti after the earthquake and claimed hundreds of lives, many wondered what caused the epidemic, which had not been seen in Haiti for more than a century. Eric E. Schadt, PhD, from Pacific Biosciences in Menlo Park, California, and colleagues compared the genomes of 5 strains of the cholera bacteria, Vibrio cholerae, using real-time DNA sequencing to assess the likely origin of the cholera outbreak. Their study was published in the January 6, 2011, issue of the New England Journal of Medicine.

Stool samples of 2 patients with a clinical diagnosis of cholera in Haiti were cultured, and V cholerae was isolated. Isolates from stool samples from other cholera epidemics, including the 1971 and 2008 outbreaks in Bangladesh and the 1991 outbreak in Peru, were used as active comparators. DNA libraries from these bacteria were constructed. The researchers found that the genome of the bacterium responsible for the current outbreak in Haiti is nearly identical to the one responsible for the past outbreaks in Bangladesh, with the same antibiotic sensitivities and virulence. This strongly suggests that the epidemic began with introduction of the cholera strain into Haiti “by human activity from a distant geographic source.”

As scientists grapple with producing an effective cholera vaccine, the authors note the “policy implications” of their study. “The apparent introduction of cholera into Haiti through human activity emphasizes the concept that predicting outbreaks of infectious diseases requires a global rather than a local assessment of risk factors,” they said.

Change in Vaccine Protocol Shows Its Merits

In 2006, in response to ongoing outbreaks of varicella, specialists from the Centers for Disease Control and Prevention updated their guidelines for immunization with the varicella vaccine to include a second dose. In order to assess the effectiveness of this change, Eugene D. Shapiro, MD, from Yale University School of Medicine, and colleagues designed a case-control study and identified children 4 years and older with varicella. The researchers measured the effectiveness of 2-dose vaccination using exact conditional logistic regression.

Published in the Journal of Infectious Diseases on February 1, 2011, the study matched 71 case subjects with 140 controls by age and pediatric practice. The researchers found that no cases of varicella were reported in patients receiving 2 doses of vaccine compared with 22 controls (15.7%); 66 cases (93%) of varicella were reported compared with 117 controls (83.6%) who had received 1 dose; and 5 cases (7%) of varicella were reported compared with 1 control (0.7%) who did not receive any vaccine. The effectiveness of 2 doses of the vaccine was calculated at 98.3% (95% confidence interval, 83.5%-100%; P <0.001). Further, a matched odds ratio of 0.053 (95% CI, 0.002-0.320, P <0.001) was calculated for 2 doses versus 1 dose.

The authors point out it is unclear why 1 dose of varicella vaccine may seem to have suboptimal effectiveness, and whether it was due to “primary vaccine failure, waning immunity, or both.” Not only are 2 doses of vaccine effective in preventing varicella, but they may also lower the risk of developing zoster, or shingles, later in life by preventing a latent infection with wildtype disease.

Children with Ear Infections Benefit from Antibiotics

Acute otitis media in children may benefit most from antimicrobial therapy, according to a study published in the New England Journal of Medicine on January 13, 2011. Researchers from Turku University Hospital in Finland designed a randomized, double-blind intent-to-treat trial enrolling 319 children between 6 and 35 months of age with a diagnosis of acute otitis media. The patients received either amoxicillin/clavulanate 40/5.7 mg/kg/day in 2 divided doses or placebo for 7 days. The primary outcome of the study was time to treatment failure from the first dose to the end-of-treatment visit on day 8.

A significant difference was seen between the groups; treatment failure occurred in 30 children who received amoxicillin/ clavulanate and in 71 children who received placebo (P <0.001). With further statistical analysis, the researchers found that amoxicillin/clavulanate had reduced the risk of treatment failure by 62% (hazard ratio, 0.38; 95% confidence interval, 0.25-0.59; P <0.001) and that to avoid treatment failure in 1 child, 3.8 children would need to be treated with amoxicillin/clavulanate.

Although other studies have shown a benefit to a “watchful waiting” approach, this study shows a much higher failure rate in the placebo group. The researchers concluded that antibiotic therapy is superior to watchful waiting in cases that can be definitively diagnosed as otitis media. PT

Fast Fact: Seasonal influenza usually reaches its peak by January, but the Centers for Disease Control and Prevention predict this year’s peak will be much later in the season.