Understanding Pneumococcal Disease; Study Sheds Light on Transmission Dynamics

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Posted on December 20, 2013

Winter is here and with the cold temperatures and the holidays come the seasonal epidemics of pneumococcus, a potentially deadly disease for the young and the elderly.

And while the arrival of the disease is reliably predicted each passing year, the precise factors that affect its rapid transmission from person to person remain poorly understood.

New research led by the Yale School of Public Health sheds light on what drives seasonal variations of the bacterial pathogen and provides information that may enhance the effectiveness of vaccine delivery. The results were published recently in the journal Clinical Infectious Diseases.

Led by Assistant Professor Daniel M. Weinberger, the study examined data from children under 7 years old in two distinct populations—the Navajo and White Mountain Apache in the southwestern United States. The researchers sought to determine whether the increase in seasonal transmission of the bacteria or increases in viral activity are related to an accompanying increase in disease cases. Few previous studies have explicitly examined this relationship.

“The impact of the pneumococcal vaccine against pneumonia has been less impressive than against bloodstream infections. We are trying to understand the risk factors for different forms of the disease to try to determine why vaccination might have less of an impact against some outcomes,” said Weinberger, who collaborated on the study with six colleagues from the National Institutes of Health, the Johns Hopkins Bloomberg School of Public Health and the Agency for Healthcare Research and Quality.

The harboring of a potentially disease-causing organism, known as carriage, is considered to be a prerequisite for pneumococcal disease and the majority of young children carry the bacteria, often asymptomatically, in their nasopharynx and inadvertently infect others.

Weinberger and colleagues found that the prevalence of pneumococcal carriage and the incidence of an invasive form of the disease, known as IPD, both varied seasonally among the children studied. They also found that seasonal variations in the occurrence of non-pneumonia IPD were associated with changes in carriage prevalence, while seasonal variations in blood-based pneumonia were associated with an important respiratory virus.

The results suggest that while carriage is likely necessary to cause pneumococcal pneumonia, in itself it is insufficient.  Viral infections, or some other seasonal risk factor, are also needed.

“We think these findings might suggest that the virus allows less virulent bacterial strains to cause pneumonia, which might undermine the impact of the vaccine,” Weinberger said. “Future work will focus on the how viral infections might shape the impacts of pneumococcal disease in different risk groups.”

Source: Yale University