Despite Vaccine, Some at Risk for Invasive Pneumococcal Disease

SAN FRANCISCO — The highest rates of invasive pneumococcal disease were seen in children younger than 2 years of age in a Massachusetts study, Dr. Katherine K. Hsu reported during a poster session at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy.

The results also showed that black and Hispanic children remain especially vulnerable to nonvaccine-type invasive pneumococcal disease (IPD), compared with white children.

“The implications in Massachusetts are that despite advances with pneumococcal conjugate vaccine and huge declines in invasive pneumococcal disease, there still are some children at risk,” Dr. Hsu said in an interview.

Using microbiology reports of pneumococcal isolates from the Massachusetts Department of Public Health, the researchers identified 357 cases of IPD in children younger than 18 years of age between Oct. 1, 2001, and Sept. 30, 2005. Demographic data was confirmed with follow-up telephone interviews with primary care providers and/or adult caregivers. Incidence rates were derived using Census 2000 denominators.

Dr. Hsu and her associates found that the relative risk of IPD was 15.9 for children younger than 6 months, 16.8 for those aged 6–12 months, and 12.7 for those aged 12–24 months, compared with a relative risk of only 4.5 for children aged 24–60 months. Dr. Hsu did not give any data on older children.

The researchers also found that black and Hispanic children were two times more likely than their white counterparts to have IPD, particularly the nonvaccine type. Dr. Hsu, of the section of pediatric infectious diseases at Boston Medical Center, noted that these differences could not be attributed to unequal vaccination coverage rates. “Are these children perhaps more at risk because they're colonized more in the nasopharynx?” she asked. “Are they from different socioeconomic classes where there's more crowding or more smoking, or are there other risk factors for invasive disease such as HIV infection that are more dominant in those populations? We don't know the answer.”

The study was supported by Wyeth.

Higher risk of IPD in black and Hispanic children could not be attributed to unequal vaccination. DR. HSU