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Respiratory infections in diabetes: Reviewing the risks and challenges

Respiratory infections in diabetes: Reviewing the risks and challenges

ABSTRACT: Although the organisms that cause community-acquired pneumonia are similar in diabetic and nondiabetic patients, those who have diabetes mellitus (DM) may have more severe disease and a poorer prognosis. Elevated blood glucose levels are associated with worse outcomes in patients with pneumonia, and the mortality risk may be as high as 30% in patients with uncontrolled DM. Thus, appropriate treatment- and possibly prevention-of bacterial pneumonia should include aggressive efforts directed at glycemic control. Other respiratory infections, such as influenza, tuberculosis, and fungal pneumonia, also are associated with greater morbidity in patients with DM. Diabetic patients with tuberculosis are more likely to present with bilateral lung involvement and pleural effusions. (J Respir Dis. 2008;29(7):285-293)

Diabetes mellitus (DM) is a complex metabolic disorder that is characterized by hyperglycemia and is associated with increasing incidence, morbidity, and mortality. According to the World Health Organization (WHO), 180 million persons have DM and 5% of deaths worldwide can be attributed to this disease. Also, there is evidence that DM is associated with an increased risk of infections and with more severe clinical consequences of such infections.1-3

The mechanisms that lead to excess morbidity and mortality are related in part to the host immune defects associated with DM. Coexisting conditions, such as vascular, renal, and cardiovascular diseases, and the various interventions associated with such diseases, contribute significantly to the increased incidence and complexity of infections in patients with DM.

In this article, we will briefly review the immunological and respiratory changes associated with DM. Then we will focus on the challenges of community-acquired pneumonia (CAP) and nosocomial pneumonia in patients with DM.

EFFECTS OF DIABETES

Immunological changes

The airways and alveoli are constantly exposed to microbes, but normal host defense mechanisms can often protect the lungs. In the upper respiratory tract, aerodynamic filtration, mucociliary clearance, cough mechanism, and neurological reflexes prevent aspiration and remove large particles.4 In the lower respiratory tract, defenses include bronchus-associated lymphoid tissue, opsonins (IgA and IgG), surfactant, extracellular chemotactic factors, alveolar macrophages, and pathogen-specific immune responses involving dendritic cells and T and B lymphocytes.5

Overall, the immune response is impaired in persons with DM. Several aspects of cellular immune function—chemotaxis, adherence, phagocytosis, and intracellular killing—are adversely affected by hyperglycemia. Anaerobic conditions in the tissue that are created by vascular compromise and inflammatory response further impair the immune response.

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