Investigation of the risk factors for tuberculosis: a case-control study in three countries in West Africa

BACKGROUND

Host-related and environment-related factors have been shown to play a role in the development of tuberculosis (TB), but few studies were carried out to identify their respective roles in resource-poor countries.

METHODS

A multicentre case-control study was conducted in Guinée, Guinea Bissau, and The Gambia, from January 1999 to March 2001. Cases were newly detected smear positive TB patients. Two controls were recruited for each case, one within the household of the case, and one in the community.

RESULTS

Regarding host-related factors, univariate analysis by conditional logistic regression of 687 matched pairs of cases and household controls showed that TB was associated with male sex, family history of TB, absence of a BCG scar, smoking, alcohol, anaemia, HIV infection, and history and treatment of worm infection. In a multivariable model based on 601 matched pairs, male sex, family history of TB, smoking, and HIV infection were independent risk factors of TB. The investigation of environmental factors based on the comparison of 816 cases/community control pairs showed that the risk of TB was associated with single marital status, family history of TB, adult crowding, and renting the house. In a final model assessing the combined effect of host and environmental factors, TB was associated with male sex, HIV infection, smoking (with a dose-effect relationship), history of asthma, family history of TB, marital status, adult crowding, and renting the house.

CONCLUSION

TB is a multifactorial disorder, in which environment interacts with host-related factors. This study provided useful information for the assessment of host and environmental factors of TB for the improvement of TB control activities in developing countries.

Risk factors for tuberculosis infection in sub-Saharan Africa: a contact study in The Gambia

Few studies have investigated the risk factors for tuberculosis (TB) infection in highly endemic countries. We conducted a household study in The Gambia, in which a tuberculin skin test (TST) was performed in members of the households of 315 smear-positive pulmonary TB cases and 305 community control subjects. The risk of being TST positive (10 mm or more) was higher in contacts of cases than in contacts of control subjects. It increased with age, male sex, and duration of stay in the household but was not associated with the presence of a bacille de Calmette-Guérin scar. Within the households of the TB cases, the risk of TST positivity was higher in males and was increased with age, social proximity to the case, and the radiologic extent of the disease in the case's chest X-ray. Adjusting on these, the risk of TST positivity was higher in first-degree relatives compared with more distant relatives and nongenetically related household members, but the effect was not statistically significant. In highly endemic areas, the risk of TB infection in contacts of TB infectious cases is associated with age, sex, intensity of exposure to the case, and severity of disease in the case, but it is possible that genetic factors contribute to the susceptibility to Mycobacterium tuberculosis infection.

Gamma interferon responses induced by a panel of recombinant and purified mycobacterial antigens in healthy, non-mycobacterium bovis BCG-vaccinated Malawian young adults

We have previously shown that young adults living in a rural area of northern Malawi showed greater gamma interferon (IFN-gamma) responses to purified protein derivatives (PPD) prepared from environmental mycobacteria than to PPD from Mycobacterium tuberculosis. In order to define the mycobacterial species to which individuals living in a rural African population have been exposed and sensitized, we tested T-cell recognition of recombinant and purified antigens from M. tuberculosis (38 kDa, MPT64, and ESAT-6), M. bovis (MPB70), M. bovis BCG (Ag85), and M. leprae (65 kDa, 35 kDa, and 18 kDa) in >600 non-M. bovis BCG-vaccinated young adults in the Karonga District of northern Malawi. IFN-gamma was measured by enzyme-linked immunosorbent assay (ELISA) in day 6 supernatants of diluted whole-blood cultures. The recombinant M. leprae 35-kDa and 18-kDa and purified native M. bovis BCG Ag85 antigens induced the highest percentages of responders, though both leprosy and bovine tuberculosis are now rare in this population. The M. tuberculosis antigens ESAT-6 and MPT64 and the M. bovis antigen MPB70 induced the lowest percentages of responders. One of the subjects subsequently developed extrapulmonary tuberculosis; this individual had a 15-mm-diameter reaction to the Mantoux test and responded to M. tuberculosis PPD, Ag85, MPT64, and ESAT-6 but not to any of the leprosy antigens. We conclude that in this rural African population, exposure to M. tuberculosis or M. bovis is much less frequent than exposure to environmental mycobacteria such as M. avium, which have antigens homologous to the M. leprae 35-kDa and 18-kDa antigens. M. tuberculosis ESAT-6 showed the strongest association with the size of the Mantoux skin test induration, suggesting that among the three M. tuberculosis antigens tested it provided the best indication of exposure to, or infection with, M. tuberculosis.

Risk factors for tuberculosis infection in children in contact with infectious tuberculosis cases in the Gambia, West Africa

OBJECTIVE

Tuberculosis (TB) infection is highly prevalent in developing countries. As infected children represent a large proportion of the pool from which TB cases will arise, knowledge of the factors that influence TB infection in children are of importance to evaluate transmission of infection in the community and adapt TB control activities. There are limited data on the risk of infection in child populations in developing countries.

METHODS

We performed a household contact study in The Gambia (West Africa), in which children who were living in contact with individuals who had proven smear-positive pulmonary TB cases were investigated. A questionnaire was addressed to the mother or caregiver of the child to investigate the presence of various risk factors and assess the degree of exposure of the child to the individual with TB within the household. A tuberculin skin test (TST) was performed on each child. TST sizes > or =5 and 10 mm, respectively, were considered positive.

RESULTS

Households of 206 TB cases were visited, and 384 children aged <5 years were examined. The median age was 2, and 48% were girls. The distribution of TST responses followed a bimodal pattern, with 135 (35%) children presenting a palpable induration. Random effects logistic regression analysis demonstrated that the risk of positive TST response in the child increased with the geographic proximity of the child to the individual with TB within the household and with the degree of activities shared with the individual with TB. It was also associated with the clinical severity of the disease in the index case. Nutritional status and presence of a bacille Calmette-Guérin (BCG) scar were not independent risk factors for TST positivity in this population. On multivariate analysis, the effect of geographic proximity to the individual with TB, household size, and duration of cough in the index case persisted for TST responses > or =5 mm.

CONCLUSIONS

In a highly endemic country with high BCG vaccination coverage in Africa, TB infection in children who were in contact with individual with infectious TB was directly related to the intensity of exposure of the child to the individual with TB. Our data suggest that a positive TST in a child reflects most probably TB infection rather than previous BCG vaccination. Contact tracing can play a major role in the control of TB in developing countries.

Mycobacterium vaccae (SRL172) immunotherapy as an adjunct to standard antituberculosis treatment in HIV-infected adults with pulmonary tuberculosis: a randomised placebo-controlled trial

BACKGROUND

Mortality rates of HIV-infected patients treated for tuberculosis remain high. This study aimed to assess the effect on mortality of immunotherapy with single-dose SRL172 added to standard antituberculosis chemotherapy in such patients.

METHODS

The double-blind trial enrolled 1229 patients aged 18-60 years, who had never received antiretroviral treatment and who presented with newly diagnosed, sputum-smear-positive pulmonary tuberculosis to referral centres in Lusaka, Zambia, and Karonga, Malawi. Both HIV-positive and HIV-negative patients were enrolled, to avoid stigmatisation. Participants were randomly assigned a single injection of SRL172 or matching placebo within 2 weeks of starting 8 months of antituberculosis chemotherapy and followed up for at least 12 months. The primary endpoint was time to death in the HIV-infected population. Analyses were based on 760 HIV-positive patients after exclusion of 84 patients with errors in storage of the injection, no bacteriological confirmation, or no HIV result.

FINDINGS

Of 760 HIV-infected patients, 374 received SRL172 and 386 received placebo. SRL172 did not cause any serious adverse events. The follow-up rate was 88% at 12 months in both groups. Of the HIV-positive patients, 109 (19.5 per 100 person-years) of 372 assigned SRL172 and 107 (19.3 per 100 person-years) of 386 assigned placebo died. In the Cox's regression analysis, stratified by centre, the hazard ratio of deaths (SRL172/placebo) was 1.03 (95% CI 0.79-1.35). There was no evidence of benefit to the group assigned SRL172.

INTERPRETATION

Immunotherapy with single-dose SRL172 as an adjunct to standard antituberculosis treatment in HIV-positive adults with pulmonary tuberculosis had no significant effect on survival or bacteriological outcome, though the treatment was safe and well tolerated.

The spectrum of dermatophytes in northern Malawi (Africa)

Between 1.5% and 2.5% of the population in Karonga District, northern Malawi (Africa), were diagnosed as having tinea faciei, corporis, inguinalis or cruris in the course of a total population survey carried out between 1987 and 1989. With regard to the relative frequency distribution of dermatophytes, the main findings were the rarity of Trichophyton rubrum (around 1%) and the predominance of Microsporum audouinii (57%) in this part of Africa. In the genital area Epidermophyton floccosum was the most common isolate (56%).

Microsporum nanum--a report from Malawi (Africa)

Microsporum nanum Fuentes 1956 has been identified in scrapings from a skin lesion in a patient in Karonga District, Malawi, Africa. We believe that this is the first such identification from the African continent. The patient had a single skin lesion in his popliteal fossa and was known to rear pigs.