Page 117 - AIDSBK23C

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BACTERIAL INFECTIONS SEEN WITH AIDS

Bacterial infections can be frequent and clinically significant in persons with HIV
infection because of the defects in both humoral as well as cell-mediated immunity late in the
course of AIDS. Recurrent bacterial infections in children and recurrent pneumonia in adults
may be used to define AIDS by CDC criteria.[389,390,391,392] The chronically debilitating
course of AIDS along with multiple drug therapies, including the use of indwelling catheters, and
the potential for superinfection of existing lesions all enhance susceptibility to bacterial
infection. In fact, during the course of infection with HIV, bacterial infections can be more
common than parasitic, viral, or fungal infections. Bacterial bronchopneumonia is second only
to Pneumocystis jiroveci (carinii) pneumonia in frequency as a cause of death from pulmonary
infections in persons with AIDS.[417] The neutropenia that may occur with AIDS, either as a
consequence of HIV infection or as a complication of drug therapy, significantly increases the
risk for bacterial infections when the absolute neutrophil count diminishes below 750/µL, and
particularly when the count is below 500/µL.[497]
The bacterial species most often responsible for nosocomial pulmonary infections are
Staphylococcus aureus and Pseudomonas aeruginosa. Community acquired pneumonia is most
frequently cause by Streptococcus pneumoniae. Other agents may include Haemophilus
influenzae and enteric bacterial species. Prophylactic vaccination for S pneumoniae and H
influenzae can reduce the incidence of these infections significantly. The host response to
infection with these agents is mainly neutrophilic, but is blunted late in the course of AIDS by
the generalized failure of the immune system. Diagnosis is made by gram stain and culture of
body fluids and tissues.[498,499,500]
Bacterial organisms in persons with AIDS most often produce respiratory disease,
particularly bronchopneumonia that can be life-threatening, but such infections can become
disseminated as well, and recurrence is common. The bronchopneumonias seen with AIDS can
be extensive and bilateral. Mortality is higher than in non-HIV-infected patients. Critically ill
HIV/AIDS patients with sepsis have greatly increased risk for mortality.[501] Bacterial
septicemias are the immediate cause of death in about 5% of AIDS patients.[417] Indwelling
catheters may predispose to infection, particularly with Staphylococcus organisms.[498,500]
Nosocomial infections are more common in patients with AIDS from immunosuppression, prior
antibiotic treatment, and greater exposure to invasive devices such as indwelling catheters. The
incidence of nosocomial infection seen with AIDS ranges from 7.9 to 15 per 100 admissions,
with bloodstream infections the most frequent, mainly due to intravascular catheters, followed by
urinary and respiratory tract infections.[502]
Two bacterial agents found in soils that can infect patients with HIV infection are Listeria
and Rhodococcus. Listeria monocytogenes, which appears as a short gram-positive bacillus,
occurs occasionally in HIV-infected patients, usually as meningitis, septicemia, or
gastrointestinal infection. Listeriosis may not be frequent because Listeria is inhibited in vivo by
tumor necrosis factor (TNF), and patients with AIDS typically have increased levels of TNF.
However, the incidence of listeriosis in persons with HIV infection and with AIDS is about 10
and 100 times respectively that of the population as a whole. Rhodococcus equi is a weakly
acid-fast pleomorphic gram-positive coccobacillary agent. The persistence of Rhodococcus in
macrophages makes its eradication in patients with a poor cellular immune response difficult and
leads to chronic relapsing infections, typically pneumonias and septicemias.[499,503,504] This