High prevalence of asymptomatic TB in HIV patients in Cape Town

HIV-positive patients in South Africa who are not yet taking antiretroviral therapy have a high prevalence of asymptomatic tuberculosis (TB), investigators report in Thorax.

Sputum screening showed that 8.5% of patients had TB, without having any symptoms of the infection . A lower CD4 cell count and longer duration of HIV were both associated with an increased risk of asymptomatic TB.

“This study found a high prevalence…of subclinical TB disease in HIV-1 infected persons. The results suggest that, in high HIV/TB endemic settings, a positive HIV-1 test should prompt TB screening by sputum culture irrespective of symptoms,” comment the international team of investigators.

Worldwide, TB is the single biggest cause of serious illness and death in patients with HIV.

Investigators wished to determine the prevalence and outcomes of asymptomatic TB in HIV-positive patients who were not yet taking antiretroviral therapy.

Their study involved 274 individuals who received care at the Khayelitsha Day Hospital, Cape Town, South Africa, between 2008 and 2010.

All the patients were screened for symptoms of TB (cough, fever, night sweats, weight loss) and provided sputum samples. Individuals also had a tuberculin skin test.

Overall, 8.5% of patients were diagnosed with TB after sputum analysis or chest x-ray. The investigators found that 22% of these patients had smear-positive TB and were “therefore more infectious.”

Although none of the patients had symptoms at the time of their diagnosis, 56% developed symptoms between three days and two months later.

“This suggests an increasing bacterial load after initial screening and that screening before the likely development of symptoms was beneficial in indicating the presence of actively replicating bacilli,” comment the authors. “This early diagnosis resulted in patients receiving treatment for TB earlier than would otherwise have occurred.”

The patients had a median CD4 cell count of 250 cells/mm³, and their median age was 34 years.

A higher proportion of TB patients had a CD4 cell count below 200 cells/mm³ than non-TB patients (39% vs 20%; p = 0.055). Patients with TB were also more likely to have a highly reactive tuberculin skin test (p = 0.051).

A number of factors had non-significant associations with an increased risk of asymptomatic TB, including a positive tuberculin skin test (p = 0.064), longer duration of HIV infection (p = 0.056), and a lower CD4 cell count (p = 0.06).

“There was a 5% decrease in TB risk for every increase in the CD4 cell count of 10 cells/mm³, and an increase of 24% in the risk of TB disease for every year after HIV-1 diagnosis,” observe the authors.

Sixteen patients started and completed TB therapy, and the 60% of individuals who were eligible initiated antiretroviral therapy.

The investigators recommend that all patients with HIV should have their sputum screened for TB, irrespective of symptoms. However, they acknowledge that this could prove difficult in some resource-limited settings. They therefore believe their results “highlight the need for new rapid and affordable point-of-care diagnostic tests to identify persons with clinical and subclinical TB disease.”