Research issues involving HIV-associated tuberculosis in resource-poor countries

CCR5 is the major coreceptor used by HIV-1 subtype C isolates from patients with active tuberculosis

Tuberculosis (TB) is the major opportunistic infection of HIV-infected patients in developing countries and is associated with activation of the immune system and increased HIV-1 expression. The aim of this study was to explore the biological properties of HIV-1 isolates from patients with active TB. Ten HIV-1 subtype C isolates were analyzed for biological phenotypes, using MT-2 cells, and for coreceptor usage, using coreceptor-transfected cell lines. All isolates were nonsyncytium inducing (NSI) in the MT-2 assay and replicated in CCR5-expressing cells. None of the isolates used CXCR4 or any of the minor coreceptors (CCR1, CCR2b, or CCR3) efficiently. Analysis of the V3 region showed that all isolates contained the GPGQ motif characteristic of subtype C and also had a sequence profile typical of NSI viruses. These data indicate that despite their advanced disease state, patients with TB harbor viruses that use the CCR5 coreceptor. It is possible that activation of monocytes and macrophages during TB infection results in the expansion of macrophage-tropic isolates that preferentially use CCR5.

Tuberculosis and the HIV epidemic: increasing annual risk of tuberculous infection in Kenya, 1986-1996

OBJECTIVES

The purpose of this study was to assess the impact of the increased incidence of tuberculosis (TB) due to HIV infection on the risk of TB infection in schoolchildren.

METHODS

Tuberculin surveys were carried out in randomly selected primary schools in 12 districts in Kenya during 1986 through 1990 and 1994 through 1996. Districts were grouped according to the year in which TB notification rates started to increase. HIV prevalence in TB patients and changes in TB infection prevalence were compared between districts.

RESULTS

Tuberculous infection prevalence rates increased strongly in districts where TB notification rates had increased before 1994 (odds ratio = 3.1, 95% confidence interval = 2.3, 4.1) but did not increase in districts where notification rates had increased more recently or not at all. HIV prevalence rates in TB patients were 50% in districts with an early increase in notification rates and 28% in the other study districts.

CONCLUSIONS

Countries with an increasing prevalence of HIV infection will need additional resources for TB control, not only for current patients but also for the patients in additional cases arising from the increased risk of TB infection.

Differences in tuberculosis incidence rates in township and in rural populations in Ntcheu District, Malawi

There has been a large upsurge of tuberculosis (TB) in many countries in sub-Saharan Africa, mainly as a result of the co-existing human immunodeficiency virus (HIV) epidemic. Malawi has had a well-run National TB Control Programme (NTP) with good registration and recording of cases. For some years the NTP has had the impression that TB in the country is concentrated around townships and is less prevalent in the rural areas. This impression was investigated in a rural district (Ntcheu District) in Malawi. Data on new TB cases were collected from the district TB register for the years 1992-96 and average annual TB incidence rates per 100,000 for semi-urban and rural populations were calculated for this period. There was a significantly higher incidence of TB, particularly amongst cases with smear-negative pulmonary TB and extrapulmonary TB, in the semi-urban population compared with the rural population. Possible explanations could be higher HIV seroprevalence rates in semi-urban areas compared with rural areas, under-diagnosis at health centres or poor access to medical facilities for rural people.

Tuberculosis in health care workers in Malawi

Although sub-Saharan Africa has the highest rates of tuberculosis (TB) and human immunodeficiency virus (HIV) infection in the world, the rates of TB amongst its health care workers (HCWs) are poorly documented. We therefore conducted a country-wide investigation. All district/government and mission hospitals in Malawi that diagnose and care for TB patients were visited in order to obtain information on hospital-based HCWs and their incidence of TB in 1996. Hospital TB case loads, country-wide TB notification numbers and national population estimates for 1996 were obtained, which enabled TB case notification rates to be calculated. In 1996, 108 (3.6%) of 3042 HCWs from 40 hospitals were registered and treated for TB: 22 with smear-positive pulmonary TB (PTB), 40 with smear-negative PTB and 46 with extrapulmonary TB. The overall case fatality rate was 24%. Compared with the adult general population aged > or = 15 years, the relative risk [95% confidence interval (CI)] in HCWs of all types of TB was 11.9 [9.8-14.4], of smear-positive PTB 5.9 [3.9-9.0], of smear-negative PTB 13.0 [9.5-17.7] and of extrapulmonary TB 18.4 [13.8-24.6], P < 0.05. The 1996 hospital TB case load ranged from 29 to 915: there were no cases of TB in HCWs in hospitals whose case load was < or = 100 patients, while the TB case rate among HCWs was similar in hospitals with annual case loads of 101-300 or > 300. The annual risk of TB was high among all categories of HCW, especially clinical officers. This study shows a high rate of TB in HCWs in Malawi, and emphasizes the need for practical and affordable control measures for the protection of HCWs from TB in low-income countries.