In this study conducted in a major referral hospital for chest diseases in Cameroon, we found a high prevalence of HIV-1 infection among patients admitted for acute community-acquired pneumonia. Half of the time, HIV infection was undiagnosed at the time of clinical presentation with CAP. Among those already diagnosed with HIV infection, about half were on antiretroviral therapy. With three exceptions, the clinical, radiological, biological profiles of patients and outcomes of care for CAP were similar between patients with HIV infection and those without. These exceptions relate to the low haemoglobin level and low total leucocytes counts in HIV positive patients and a high complication rates among HIV negative patients.
The prevalence of HIV infection in our study is about the double of the prevalence rate reported in Cameroon 15 years ago  based on 110 patients recruited from three different hospitals, probably mirroring the changing prevalence of HIV in the country between the two study periods. Indeed, available data suggest that HIV prevalence was about 3% at the general population in Cameroon in 1994 , and increased to about 5% in 2007 . Otherwise, HIV prevalence in our study was closer to the 58% rate reported by Horo et al.  in Ivory Coast .
While the well-known young age of patients with HIV may explain part of the findings, our study suggests that hospitalised patients with CAP in this setting were predominantly young individuals. This may reflect the overall young age of the general population. The equal distribution of women among HIV negative and HIV positive patients suggests that high rates of HIV infections among women in Africa  may not necessarily translated into more women with HIV developing CAP. Such a claim however, based on a hospital cohort remains very weak in the context of many uncontrolled sources of biases. The broadly comparable clinical and radiological profiles of patients with and without HIV infection found in our study is in agreement with existing reports[1, 3]. Of note, the disease severity as assessed by the CRB-65 score  was unaffected by HIV status. Differences found in the haematological profile were largely expected. For instance, it is well known that anaemia is of multifactorial causes in the context of HIV infection, and is not necessarily correlated with immune-depression and presence of opportunistic infections [17, 18].
The comparable evolution and outcomes of patients regardless of their status for HIV in our sample is largely in agreement with earlier report from the same setting . The high prevalence of loco-regional complications among HIV negative participants in this study is possibly related to a high prevalence of infections due to necrotizing micro-organisms in this subgroup. Indeed, in a recent study on purulent pleural effusions in the same setting, we found that Staphylococcus aureus micro-organism was more frequently isolated in HIV negative than in HIV positive patients (23.8% vs. 12.5%), although the difference was not statistically significant, due to the small sample . However, death rate among our much large sample of patients with HIV infection was likely higher than the 7% reported previously based on half the size of our cohort with HIV . Discrepancies are likely due to difference in precisions on the diagnosis of CAP. The former study  used microbiological investigations for diagnosis confirmation and accordingly adapting treatments, what our study did not afford. In over half of patients with fatal outcomes in our sample, death occurred with the first 72 h of observation needed to assess the response to treatment. Some would have been the result of inappropriate initial diagnosis or inefficacy of the empirical treatment. In general mortality rate among HIV patients with CAP across published data varies substantially [5, 7, 8, 20–22]. However, available studies on the effect of HIV on fatal outcome in patients with CAP are conflicting with some suggesting a less favourable outcome in patients with severe immune depression [5, 21, 23], and others suggesting no effect of immune depression on mortality [1, 6, 7, 23]. In a study by Feldman et al.  in HIV positive patients with bateriemic pneumococcal pneumonia, fatality rate was high in patients with severe immune-depression. We instead found no significant difference in death rates among patients CAP patients with HIV according to the severity of the disease (data not shown).
Our study has some limitations including the retrospective nature and as a result data were missing for some participants on some variables including key inclusion variables such as HIV status, HIV viral load and other variables like nutitional and socioeconomic status. In the absence of microbiological investigations, we were unable to have a definitive confirmation of diagnosis. In this context, some patients would have probably been misclassified as having CAP or not, which may have the undesirable effect of biasing the results if occurring in a differential ways. The previous study in this setting suggests using microbiological diagnosis as a standard, physicians diagnosis of pneumonia is accurate in about 50% of cases, and similarly among patients with HIV and those without . The strengths of our study include the relatively larger number of people with HIV and accordingly more power to investigate the effects of prior knowledge of HIV status on clinical presentation and outcome of care for CAP.
In conclusion, HIV infection is highly frequent among patients with CAP in this setting. In major ways however, it seems to be unrelated with key aspects of the disease including clinical presentation, radiological findings, response to empirical antibiotic treatment and fatal outcomes. Therefore similar strategies should be applied to CAP patients regardless of the status for HIV. However, CAP presentation should be used as an opportunity to screen individuals for undiagnosed HIV infection. Larger prospective studies and needed to consolidate these findings.