Tuberculosis (TB) is the commonest opportunistic infection and the number one cause of death in HIV patients in developing countries, and accounts for about 40% of all manifestations seen in HIV patients [1]. About 25% to 65% of patients with HIV/AIDS have tuberculosis of any organ and tuberculosis accounts for about 13% of all HIV related deaths world wide [2–6]. While tuberculosis prevalence has declined by more than 20% worldwide, the rates in Africa have tripled since 1990 in countries with high HIV prevalence and are still rising across the continent at 3–4% per year [7]. Between 1998 and 1999, a 20% increase of tuberculosis cases was reported in countries severely affected by HIV/AIDS in Africa[8]. Correct diagnosis and treatment of tuberculosis help to reduce the burden of tuberculosis, provided that infectious cases are detected and treated successfully. However, there are difficulties in achieving the goal of reducing the tuberculosis burden due to a number of challenges, such as difficulties in diagnosing tuberculosis in HIV infected patients due to unusual clinical picture with increase in smear negative acid fast bacilli (AFB negative) pulmonary tuberculosis disease, and atypical findings on chest radiography [9, 10]. People with HIV are increasingly infected with tuberculosis because HIV weakens their immune system[11] HIV/AIDS fuels the tuberculosis epidemics in many ways, such as promoting progression to active tuberculosis, increasing the risk of reactivation of latent tuberculosis infection, as well as increasing chance of tuberculosis infection once exposed to tubercle bacilli [3, 12]. Autopsy studies have shown disseminated tuberculosis in 14–54% of HIV infected people in HIV prevalent countries, many of whom were undiagnosed prior to death [13]. The prevalence of tuberculosis in HIV patients on care and treatment in rural Tanzania is not known. We report on the prevalence of undiagnosed tuberculosis and drug susceptibility among the HIV patients attending care and treatment clinic in rural northern Tanzania.

We found high prevalence of tuberculosis disease among HIV/AIDS patients attending care and treatment in this setting. A study done in Dar es Salaam found a prevalence of 15% in patients attending HIV care and treatment clinic[20]. Our prevalence of 8.5% is low when compared with the study done in Dar es Salaam. The difference between these two studies can be explained by the fact that Dar es Salaam is urban and contributes about 24% of all tuberculosis cases in Tanzania, while the rural area where we did our study contributes less than 2%[11]. Patients with low immunity due to HIV are more likely to acquire tuberculosis in an area with high tuberculosis prevalence. Also, the prevalence of HIV in Dar es Salaam is higher than the national average of 7%[21, 22] and higher than the prevalence of 2%[23] for the area where we did our study. This means that there are relatively more HIV patients who are susceptible to tuberculosis in Dar es Salaam than in the area of our study. The prevalence of 8.5% is lower than 40–54% found in autopsy studies done in HIV infected people who were undiagnosed prior to death[13] However, these studies included all forms of tuberculosis, while in our study we included pulmonary tuberculosis only. In another study done in Fajara Research clinic in Gambia among HIV patients who were followed at the clinic, 43.2% were diagnosed to have tuberculosis after 28 days of follow up, and 66% of them had pulmonary tuberculosis confirmed by microscopy and/or culture[24]. In yet another study done in South Africa among African gold miners the point prevalence of undiagnosed tuberculosis among HIV positive participants was 3.8% [25]. Our prevalence of 8.5% is close to 9% found in a study done in Cambodia [26]. Part of the differences between the prevalence in our study and the other studies may be due to differences in inclusion and exclusion criteria. As patients already diagnosed to have tuberculosis and started tuberculosis treatments were excluded in our study, this may have given lower rates than in some of the other studies.

Out of 20 tuberculosis patients in our study, smear was positive in 8 (40%) patients, this is close to the figure of 42% reported in Ethiopia [27]. Most of the mycobacteria isolated from these patients were susceptible to the first line tuberculosis drugs (rifampicin, streptomycin, isoniazid and ethambutol). Resistance to isoniazid was found in only one patient (5%), and no cases of multi-drug resistant tuberculosis was identified; this is similar to the report from the Tanzanian National tuberculosis control program, where 90% of all isolates were sensitive to these drugs and resistance to isoniazid was 5% [11]. However, another study done in northern Tanzania showed that among HIV tuberculosis coinfected patients resistance to at least one drug was 10.8% [28]. A study done in Mwanza Tanzania and published 10 years ago demonstrated that among HIV tuberculosis coinfected patients 13% had strains resistant to isoniazid, rifampicin, thiacetazone and/or streptomycin[29] A recent study from Cambodia shows that the resistance to anti tuberculosis drugs is decreasing since the introduction of antiretroviral drugs and there was a decrease of resistance from 48% in 1999 to 7.9% in 2004 [30].

Symptoms like fever, cough and weight loss were uncommon among tuberculosis patients in this study. This unusual presentation means that the screening of tuberculosis among HIV patients by using symptoms of fever, cough, weight loss and chest radiography with features suggestive of tuberculosis would detect only 25% of the HIV tuberculosis infected patients. This suggests that chest radiography and clinical symptoms, as recommended in Tanzania for follow up screening of HIV patients for tuberculosis, may not detect up to 75% of tuberculosis cases in people living with HIV. Eight patients with tuberculosis were on antiretroviral drugs for more than six months and yet developed tuberculosis; this shows that there is a need to do regular tuberculosis screening by sputum microscopy and culture to diagnose tuberculosis in HIV patients on treatment. Ten patients found to have tuberculosis were not yet eligible for antiretroviral drugs. If tuberculosis were diagnosed in these patients and correctly staged, they would be eligible for antiretroviral drugs and cotrimoxazole prophylaxis (CP) [11, 19, 31, 32].

Anaemia was uncommon among the study subjects, 75% of them had normal haemoglobin level. This could be due to the regular check up of haemoglobin every time the patients come to the care and treatment clinic, where those who are found anaemic are treated free of charge.

Malnutrition was found in 70% of the coinfected patients. Malnutrition and tuberculosis increases morbidity and mortality in HIV patients [31, 32]. Most of the HIV patients, irrespective of their tuberculosis status, were in WHO stage III and IV. This means that they present at hospital in late stage with advanced disease. Overall, females were more affected with HIV (71.1%) than males, may be due to the fact that females are more vulnerable to HIV than males because of their biological make up, and social and cultural factors.

A strength of our study is that the data come from a clinic that takes care of the HIV/AIDS patients daily, so our results reflect the real situation in a rural HIV clinic, though we have a small sample size. A limitation of our study is that it is hospital based and the patients included were those who were seriously ill. Thus, we might have missed the group of not seriously ill patients who opted not to attend the hospital for care. Also the culture media Lowenstein Jensen we used lacks sensitivity; in this case we might have missed some cases of tuberculosis. However in a resource poor setting countries like Tanzania the only available culture media is Lowenstein-Jensen media, therefore we used the available media to reflect the actual situation in this poor setting

We found high prevalence of tuberculosis in this setting. Chest radiographs suggestive of tuberculosis and clinical symptoms like fever and cough were uncommon findings in HIV tuberculosis coinfected patients. Tuberculosis can occur at any stage of CD4+T cells depletion.