Key Point

Asthma is an independent risk factor for invasive pneumococcal disease. Thus, vaccination should be considered for asthma patients.

NASHVILLE—Pneumococcal vaccination guidelines intentionally exclude individuals with asthma. Similarly, asthma guidelines do not recommend pneumococcal vaccination for most asthma patients.

Why the Discrimination?

It has not been conclusively proven that asthma is among those obstructive airway diseases—namely emphysema and chronic bronchitis—that raise the risk of infection with Streptococcus pneumoniae. However, it looks as if it may be time to add asthma to that list, a recent population-based study suggests.¹

“Ours is the first study to show that people with asthma, whether or not they have serious comorbidities or are on steroids, are at increased risk for the most serious type of S pneumoniae infection,” principal study author Thomas R. Talbot, MD, MPH, told Pulmonary Reviews. Dr. Talbot is Assistant Professor of Medicine and Preventive Medicine at Vanderbilt University in Nashville.

His study examined the relationship between asthma and invasive pneumococcal disease among children and adults enrolled in TennCare, Tennessee’s Medicaid program, for more than one year during a seven-year period. “We identified an increase by more than a factor of two in the risk of invasive pneumococcal disease among persons with asthma, even after adjustment for other risk factors for the disease,” the authors reported.

The observed risk increase was present among those with and without coexisting high-risk conditions and among young children, adolescents, and adults, pointed out the authors. The association between asthma and pneumococcal disease was independent of long-term corticosteroid use, they also found.

IDENTIFICATION OF PNEUMOCOCCAL DISEASE

The authors identified invasive pneumococcal disease in their subjects through the Active Bacterial Core surveillance network of the US Centers for Disease Control and Prevention, which had a surveillance population of nearly three million in Tennessee at the time of the study. Invasive pneumococcal disease was defined as the isolation of S pneumoniae from a normally sterile site such as cerebrospinal, pleural, peritoneal, pericardial, or joint fluid, blood, a surgical aspirate, or bone.

An upper age limit of 49 was chosen for the study population to reduce confounding from tobacco-related lung disease. “Children less than 2 years of age were not included, because asthma is difficult to diagnose with certainty in very young children,” related the authors.

Of the 4,581 cases of invasive pneumococcal infection that occurred in the surveillance areas during the study period, 635 were in eligible 2- to 49-year-olds in the TennCare population. Each of these cases was compared to 10 age-matched controls with no history of pneumococcal disease. The asthma rates in the two groups were 18% and 8.1%, respectively.

After adjustment for sex, race, and coexisting high-risk conditions (eg, cancer, cardiac disease, or diabetes), there was an odds ratio for invasive pneumococcal disease of 2.4 among those with asthma. “These findings were consistent in analyses stratified according to the severity of asthma, the presence or absence of coexisting high-risk conditions, and age,” said the study authors.

During the study period, the average annual incidence of invasive pneumococcal disease in the study population was 6.1 episodes per 10,000 among those with asthma versus 2.0 per 10,000 for those without asthma. The average annual incidence was 6.9 and 3.9 per 10,000, respectively, for patients with high- and low-risk asthma; the authors distinguished between the two categories of asthma based on patients’ past needs for medication, emergency care, and hospitalization.

Asthma continued to confer a significantly greater risk of invasive pneumococcal disease when individuals with coexisting high-risk conditions were excluded from the analysis. Importantly, serotype analysis indicated that most of the pneumococcal isolates obtained from asthma patients with invasive pneumococcal disease were covered by the two available pneumococcal vaccines (the conjugate vaccine and the 23-valent polysaccharide vaccine).

A PLAUSIBLE EXPLANATION

“The increased risk of invasive pneumococcal disease among persons with asthma has biologic plausibility,” the authors asserted, “because in asthma unique pathologic alterations in the airway can lead to impaired clearance of pathogenic bacteria.... Furthermore, chronic inflammation of the airway among persons with asthma and those with COPD may well contribute to impaired immunity and to a predisposition to bacterial and viral infections.”

In fact, the authors continued, the most recent recommendations from the CDC for vaccination against S pneumoniae include chronic pulmonary disease (defined as COPD or emphysema) as a risk factor for pneumococcoal disease. But the guidelines state that “asthma has not been associated with an increased risk for pneumococcal disease, unless it occurs with chronic bronchitis, emphysema, or long-term use of systemic corticosteroids.”

Not only are persons with asthma explicitly excluded from among those considered as candidates for pneumococcal vaccination, immunization against pneumococcal disease is not included in the most recently published guidelines for managing asthma, the authors pointed out.

They noted that the patients in their study most in need of the vaccine were those without other high-risk conditions for which pneumococcal vaccination is already recommended.

The study findings are especially pertinent in light of climbing asthma rates in the US, which are likely to lead to an increased burden of invasive pneumococcal disease. “It is time now for us to begin discussing the feasibility and cost-effectiveness of pneumococcal vaccination for people with asthma,” concluded Dr. Talbot. “I think our study will allow those discussions to begin.”

—Timothy Begany

Reference
1. Talbot TR, Hartert TV, Mitchel E, et al. Asthma as a risk factor for invasive pneumococcal disease. N Engl J Med. 2005;352:2082-2090.

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