Evidence supporting the notion that diabetes predisposes to an increased risk of infection continues to be inconclusive. In fact, in patients with diabetes, the percentage of outpatient visits to a physician because of an infection ranges from 1.6% to 5.1%, whereas individuals without diabetes average 2.6%–3.6% outpatient visits to physicians as a result of an infection. Additionally, compared to the general population, the percentage of deaths due to infection in those diagnosed with diabetes ranges from 2.7% to 3.4% compared to a range of 4.1% to 4.6% in individuals without diabetes. In individuals with diabetes, the mechanisms have not been clearly elucidated but are partly attributed to the effect of hyperglycemia on the immune system, increased risk of local tissue ischemia, and neuropathy. The available evidence suggests that individuals with diabetes are more likely to develop certain infections, including asymptomatic bacteriuria (especially women), urinary tract infection, pyelonephritis, renal and perinephric abscess, lower extremity infections, deep subcutaneous tissue infections, postoperative sternal wound infections, and tuberculosis compared to individuals without diabetes. In 2010, 2.8% of hospital discharges for persons diagnosed with diabetes were due to foot ulcers, a stark contrast when compared to only 0.6% of discharges due to foot ulcers in individuals without diabetes.
There is inadequate evidence linking diabetes to an increased risk of pneumonia or influenza. The case fatality rate among individuals with diabetes who are diagnosed with a respiratory tract infection, such as influenza, sinusitis, and bronchitis, ranges from 1% to 1.4% compared to a range of 1.9% to 2.4% in individuals without diabetes. Most clinical guidelines recommend persons with diabetes receive the pneumonia and influenza vaccines. Similar to the evidence linking diabetes to respiratory tract infections, the evidence linking diabetes to an increased risk of fungal infections, superficial bacterial skin and soft tissue infections, sinusitis, or bronchitis, is weak.
However, there are infections that occur almost exclusively among individuals with diabetes, including: emphysematous pyelonephritis and emphysematous cholecystitis, malignant otitis externa, and rhinocerebral mucormycosis. Additionally, diabetes has been identified as a risk factor for invasive group B streptococcal infections in nonpregnant adults. Immunological defects, microangiopathy, and autonomic and sensory neuropathy have all been implicated as risk factors for the aforementioned infections in individuals with diabetes. This chapter summarizes the body of evidence on the relationship between diabetes and infectious disease risks and outcomes.