Cigarette Smoking and Invasive Pneumococcal Disease
abstract & commentary
Synopsis: Cigarette smoking is the strongest independent risk factor for invasive pneumococcal disease among immunocompetent, nonelderly adults.
Source: Nuorti JP, et al. N Engl J Med 2000;342:681-689.
The highest incidence of invasive pneumococ-cal disease is found among young children and the elderly. The highest absolute number of infections, however, is found in nonelderly adults. Although some may have predisposing risk factors (e.g., chronic illness), many adults with invasive pneumococcal disease do not have any recognizable risk factors. The contribution of cigarette smoking to the risk of invasive pneumococcal disease is unclear though approximately half of otherwise healthy adults with invasive pneumococcal disease are cigarette smokers.
To assess the contribution of active and passive smoke to the risk of invasive pneumococcal disease, Nuorti and associates designed a population-based case-control study. This study targeted immunocompetent nonelderly adults between 18 and 64 years of age. They included only community-acquired cases of invasive pneumococcal disease, which was defined as an illness in which Streptococcus pneumoniae was isolated from a normally sterile site, such as blood or cerebrospinal fluid. Immunocompromised, immunosuppressed, and institutionalized patients were excluded. Chronic illness was present in 23%, and 28% had an indication for the pneumococcal vaccine, of which only 9% actually received the vaccine.
Among those with invasive pneumococcal disease, 57% of men, 59% of women, 64% of nonblacks, and 51% of blacks were current smokers. Among the controls, 26% of men, 26% of women, 25% of nonblacks, and 24% of blacks were current smokers. There were an equal percentage of patients and controls in both groups who were former smokers, but the average time patients had quit smoking was 11.3 years while controls had quit for an average of 17.0 years. Patients were 4.1 times as likely as controls to be current smokers. Further, a linear dose-dependent relationship was found with higher risk with increasing pack-years of smoking. Finally, for former smokers, the risk of invasive pneumococcal disease declined with increasing time since quitting.
Among nonsmokers, 33% of patients and 17% of controls were exposed to passive smoke. Those exposed to passive smoke were 2.5 times as likely to develop invasive pneumococcal disease. Individual chronic diseases (e.g., COPD, diabetes, and heart failure) did not increase the risk for invasive pneumococcal disease, but when classified as chronic illness collectively, these patients were 3.3 times as likely to develop disease. Other factors associated with invasive pneumococcal disease included living with children younger than 6 years of age who attended daycare, low socioeconomic status, male sex, black race, and low level of education.
This article examines the risk factors that can be associated with pneumococcal disease. Although multiple factors are associated with increased risk for S. pneumoniae infection, Nuorti et al conclude that cigarette smoking is the strongest independent risk factor for invasive pneumococcal disease in immunocompetent, nonelderly adults.
COMMENT By David Ost, MD, & Dheeraj Khanna, MD
One of the many health consequences of cigarette smoking is acute respiratory tract infection.1 Smoking increases the risk for community-acquired pneumonia.2 This risk is also present in the immunocompromised host, such as those infected by HIV.3 The pathophysiologic effects include: 1) alterations of central airways with loss of cilia and mucus gland hyperplasia; 2) alterations of peripheral airways with inflammation, goblet cell metaplasia, and mucus plugging; 3) alterations of alveoli and capillaries with elevated numbers of activated inflammatory cells and destruction of peribronchiolar alveoli; and 4) alterations of immune function with reduced immune response to inhaled antigens.1
This study has important implications for the practice recommendations of the pneumococcal vaccine and benefits of smoking cessation. The pneumococcal vaccine is recommended for the elderly and those with chronic illnesses; this study suggests that it may be ben-eficial in other subsets of smokers as well. The plausibility and cost-effectiveness of such strategies need to be evaluated.
References
1. Sherman CB. Med Clinics North Am 1992;76:355-375.
2. Almirall J, et al. Chest 1999;116:375-379.
3. Conley LJ, et al. AIDS 1996;10:1121-1126.
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