Immunodeficiency and Invasive Pneumococcal Disease

Abstract

This chapter focuses on the rates and clinical manifestations of invasive pneumococcal disease in patients at high risk, on proposed mechanisms of impaired defense, as well as on strategies for prevention of invasive pneumococcal disease in these groups. It describes how individual host defects may each contribute independently to the increased risk of invasive disease, and observes that the potential number of immunological risk factors is greatest and rates of invasive pneumococcal disease are highest among HIV type 1 (HIV-1). The extremely high rates of invasive pneumococcal disease in apparently otherwise healthy children suggest the presence of specific defects related to this class of organisms. HIV-1-associated immunodeficiency, rather than behavioral (e.g., smoking), medical (e.g., splenectomy, liver disease), environmental (e.g., seasonality), or bacteriological features (serotypes or colonization), appears to underlie the remarkable rates of disease in this population. Despite the many fold-increased rates of pneumonia and, particularly, invasive pneumococcal disease during HIV-1 infection, no specific overriding risk or target for intervention has been confirmed. The protection provided by both the 23-valent polysaccharide vaccine in adults and the 7-valent conjugate vaccine in children is most apparent and consistent against invasive pneumococcal disease. Specific immune defects can be identified for particular groups at higher risk of invasive pneumococcal infection, whereas more generalized deficiencies in immune and nonimmune defenses underlie bacteremia in others. The development of newer vaccines which are more universally immunogenic and which combat mucosal disease more effectively is an important goal in preventing pneumococcal disease in the immunocompromised host.