Any Evidence of an Asthma-Pneumonia Link?

Are patients with asthma at increased risk for pneumococcal infections?
— MD

The association between asthma and pneumococcal disease has been suspected by many clinicians; however, formal investigations confirming an increased risk of pneumococcal disease in patients with asthma are rare. Often, studies examining risk factors for pneumococcal disease have grouped all chronic pulmonary diseases together with no delineation of the specific type of underlying disease.

This lack of data is reflected in the most recent CDC recommendations for vaccination against Streptococcus pneumoniae.¹ These guidelines include chronic obstructive pulmonary disease as a risk factor for pneumococcal disease but 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."¹ Patients with asthma are excluded as vaccination targets.^1,2

One case-control study analyzed cigarette smoking as a risk factor for the development of invasive pneumococcal disease, such as bacteremia or meningitis.³ Asthma, distinguished from other forms of obstructive lung disease and defined by patient questionnaire, was associated with a 2.5-fold increased risk of invasive pneumococcal disease before, but not after, adjusting for other risk factors.³

We conducted a nested case-control study using data from 2 large population-based databases.⁴ The study population included persons aged 2 to 49 years. For each person with invasive pneumococcal disease, 10 age-matched controls without such disease were randomly selected from the same population.⁴ Asthma was defined by the presence of 1 hospital/emergency department (ED) diagnosis or 2 outpatient diagnoses of asthma or by the use of asthma-related medications. Persons with asthma were at increased risk for invasive pneumococcal disease (adjusted odds ratio, 2.4).⁴ The risk was greater in those with high-risk asthma (those with an asthma-related hospitalization or ED visit, use of rescue or long-term oral corticosteroids, or use of 3 or more b-agonists in the previous year). Among persons without other comorbid conditions, such as sickle cell disease or immunosuppressive disease, the incidence of invasive pneumococcal disease was 4.2 episodes per 10,000 persons with high-risk asthma and 2.3 episodes per 10,000 persons with low-risk asthma, compared with 1.2 episodes per 10,000 in persons without asthma.

The incidence of invasive pneumococcal disease in persons with asthma mirrored rates reported in other high-risk populations that are targets for pneumococcal vaccination, such as persons aged 65 years and older. Thus, asthma resulted in a greater than 2-fold increase in the risk of invasive pneumococcal disease, even after adjusting for other risk factors. The increased risk of invasive pneumococcal disease was present among those with and without other comorbid conditions and in young children, adolescents, and adults.

Defining this association allows for the addition of asthma to the list of conditions that increase the risk of invasive pneumococcal disease. These data also suggest that pneumococcal vaccination may be a worthwhile strategy for reducing the risk of invasive pneumococcal disease in persons with asthma. However, the study findings need to be independently confirmed, and more formal cost-benefit analyses are required to change current vaccine recommendations.

As the incidence of asthma continues to climb in the United States,^5,6 the burden of invasive pneumococcal disease will probably increase, and the feasibility and cost-effectiveness of pneumococcal vaccination in persons with asthma must be carefully explored.

— Thomas R. Talbot, MD
  Assistant Professor of Medicine and Preventive Medicine
  Associate Hospital Epidemiologist
  Vanderbilt University School of Medicine
  Nashville, Tenn