Population-based study of rotavirus vaccination and intussusception

BACKGROUND

During the first year that the rhesus rotavirus tetravalent vaccine (RRV-TV) was licensed, the Vaccine Adverse Event Reporting System received several reports of intussusception after vaccination. To evaluate the risk of intussusception, we conducted a retrospective cohort study in ten managed care organizations.

METHODS

Cases of intussusception were identified by searching electronic databases for diagnoses of intussusception (ICD-9 Code 560.0) in infants 1 to 11 months of age and confirmed by medical chart review. Vaccination and enrollment data were obtained from administrative databases. Incidence rate ratios (RR) of intussusception were computed by dividing incidence rates in prespecified risk intervals after vaccination by the background rate of intussusception and adjusted for age by Poisson regression. Cox proportional hazard regression was used to evaluate risk by vaccine dose.

RESULTS

Of 463,277 children 56,253 had been vaccinated with a total of 91 371 doses of RRV-TV. The incidence rate of intussusception was 25/100,000 person years among unexposed infants and 340/100,000 person years 3 to 7 days postvaccination. In the interval 3 to 7 days after vaccination, the age-adjusted RR was 16.0 (95% confidence interval, 5.5 to 46.7) for all doses combined and 30.4 (95% confidence interval, 8.8 to 104.9) after the first dose. RRs for the 8- to 14- and 15- to 21-day risk intervals were >1.0, but the confidence intervals substantially overlapped 1.0. The attributable risk was one case of intussusception per 11 073 children vaccinated.

CONCLUSIONS

RRV-TV is associated with an increased risk of intussusception. The risk is greatest 3 to 7 days after the first vaccination dose.

The inaccuracy of axillary temperatures measured with an electronic thermometer

Temperatures were measured using an electronic thermometer in an emergency department to determine the relationship between oral or rectal and axillary measurements. A total of 164 data pairs were obtained--95 in afebrile children, and 69 in febrile children. The correlation coefficient was .74 for oral-axillary pairs, and .70 for rectal-axillary pairs. The mean difference between oral and axillary temperatures was 1.17 degrees C +/- 0.72 degrees C, and between rectal and axillary temperatures was 1.81 degrees C +/- 0.97 degrees C. Using 37.4 degrees C (greater than or equal to 2 SDs) axillary as the upper limit of normal, the sensitivity, specificity, and positive and negative predictive values were calculated for detecting a fever. The sensitivity was 46%; specificity, 99%; positive predictive value, 97%; and negative predictive value, 72% for combined oral-axillary and rectal-axillary data. It was concluded that axillary temperatures are not sensitive enough to determine a fever when measured with an electronic thermometer. Electronic thermometers should be used to determine oral or rectal temperatures; axillary temperatures may be misleading and should be abandoned in the outpatient setting.