By medwireNews Reporters
Hospital admissions for Pneumocystis pneumonia (PcP) in HIV-infected individuals are significantly more common in the summer months, US research shows.
In addition, higher temperatures were independently associated with an increase in hospital admissions for PcP in an analysis of HIV+ patients in San Francisco, California, as were elevated sulfur dioxide (SO2) levels.
Each 5°F increase in temperature was associated with a significant 41% increase in the risk for hospitalization among the HIV+ patients, while each 1-unit increase of SO2 parts-per-billion was associated with a significant 80% increase in the risk for hospitalization.
"The peak of PcP admissions in the summer coincided with the peak in mean temperature," report senior researcher Peter Walzer (University of Cincinnati College of Medicine, Ohio) and colleagues in Clinical Infectious Diseases.
To identify climate and air pollution risk factors contributing to PcP, the researchers conducted a case-crossover study in 457 HIV+ patients with confirmed PcP admitted to San Francisco General Hospital between 1997 and 2008.
There was a significant difference in the number of PcP hospital admissions across the seasons, with 129 admissions occurring in the summer, 125 admissions in the spring, and 91 admissions in the winter.
In a risk model that looked at single pollutants, temperature and SO2 levels were significantly associated with PcP hospital admissions.
"Although it is difficult to explain how SO2 might increase PcP hospital admissions, it is known that exposure to SO2 in humans causes nose and throat irritation, bronchoconstriction and dyspnea," according to Walzer and colleagues.
Exposure to SO2 in animal models can lead to lung remodeling, increased mucus secretion, inflammation, airway hyperresponsiveness, and chronic obstructive pulmonary disorders, as well as an impaired alveolar macrophage response.
In the present analysis, increasing carbon monoxide levels attenuated the effect of increasing SO2 levels on the risk for PcP hospitalization.
"Unfortunately, it is difficult to find a good explanation for the association," state the researchers.
However, they suggest that carbon monoxide could prevent or reduce the temperature-induced generation of sulfates, and this results in the observed attenuation of SO2 effect.
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