Symptom screening alone can't rule out tuberculosis in HIV-infected patients, especially if these patients are on antiretroviral medications, new research shows.
"If tuberculosis screening does not include culture, a large proportion of patients with tuberculosis may be identified as TB-free and would inadvertently be placed on isoniazid monotherapy," Dr Molebogeng X. Rangaka of the University of Cape Town in South Africa, the first author of the new study, said.
Isoniazid preventive therapy (IPT), along with intensified case finding and infection control, make up the World Health Organisation's "three I's" strategy for reducing morbidity and mortality from TB in HIV patients.
In a paper online in Clinical Infectious Diseases, Dr Rangaka and his team noted that in a recent WHO meta-analysis, screening HIV-infected individuals for current cough, fever, night sweats, or weight loss had a high negative predictive value for tuberculosis - but none of the patients were on antiretroviral therapy (ART), so the diagnostic performance of the symptom screening algorithm when patients are taking ART is not clear.
Patients in the study
In the new study, the group looked at 1 429 HIV patients, 54% of whom were already taking ART. The remaining patients were being prepared for ART treatment. All underwent symptom screening and sputum culture.
Overall, 8.8% had culture-positive TB. Sensitivity of the WHO symptom screen was 23.8% for patients on ART, compared to 47.6% for the pre-ART patients. Specificity was 94.4% vs 79.8%, respectively. Among patients on ART, the probability of having TB after a negative symptom screen was 4.4%, while it was 8.9% for the patients who were not yet on ART, according to the researchers.
"Where clinics perform regular tuberculosis screening, symptomatic TB disease will be easily picked up," Dr Rangaka said via email. "The remaining pool of patients with probable disease may likely be asymptomatic - i.e., not have the typical symptoms described by the WHO screen; additional tools like culture will therefore be required to actively identify disease in this pool."
He and his colleagues conclude: "Until more sensitive methods of ruling out tuberculosis are established, it would be prudent to do a sputum culture prior to IPT where this is feasible."
(Reuters Health, Anne Harding, September 2012)
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