The study was conducted in Unit A of the Chest service of the Yaounde Jamot Hospital (YJH), the reference hospital for respiratory diseases for the capital city of Cameroon (Yaounde) and surrounding areas. In this service, the diagnosis of SPPTB is made on the basis of a suggestive clinical history and the presence of AFB on at least one of two sputum samples submitted on two consecutive days by the patient for microscopic examination, after staining by the auramine technique . Cultures for mycobacteria are hardly ever done because of costs.
All patients with a first episode of SPPTB are hospitalized during the intensive phase of treatment which lasts for two months. The total duration of treatment is six months. It consists of a two month intensive phase of daily rifampicin (R), isoniazid (H), pyrazinamide (Z) and ethambutol (E), followed by a four month continuation phase of daily R and H on outpatient basis. Treatment in the intensive phase is administered under direct supervision of the health personnel while compliance to treatment during the continuation phase is assessed by monthly return for drug collection.
During the six month treatment period, the patients’ sputum is checked thrice for the presence or absence of AFB by direct microscopic examination. This is done at the end of the two month intensive phase and at the end of fifth and sixth month of treatment. In patients whose sputum smears remain positive at the end of the two month intensive phase of treatment an additional month of intensive phase treatment is given followed by the continuation phase. The outcomes of patients at the end of the six months of treatment is recorded into one of the following six mutually exclusive categories according to the recommendations of the Union and Wold Health Organisation [1, 8] 1) cured: treatment completed with a negative sputum smear in the last month of treatment and on at least one previous occasion; 2) treatment completed: patient who has completed treatment but does not meet the criteria to be classified as a cure or failure; 3) treatment failure: patient who is sputum smear positive at five months or later during treatment; 4) died: patient who dies for any reason during the course of treatment; 5) defaulted: patient whose treatment is interrupted for two consecutive months or more; 6) transferred out: patient who has been transferred to another recording and reporting unit and for whom treatment outcome is unknown. Patients are considered as having treatment success if they fall in categories (1) and (2).
A prospective cohort of all patients aged 15 years and above, hospitalised in the service between October 2009 and May 2012 (32 months duration) with a first episode of SPPTB and whose sputum smears remained positive for AFB at the end of the two month intensive phase of treatment was studied. After obtaining informed consent, each patient’s medical records were reviewed. The following baseline information on admission was extracted from each patient’s file: age, sex, duration of illness before admission, clinical signs, alcohol and tobacco use, body mass index, HIV serostatus as well as the CD4 cell count for those with HIV infection. The result of the sputum smear of each patient with a higher bacillary load of the two examined for diagnosis as well as that of the sputum smear examined at the end of the two month intensive phase of treatment were also recorded. Bacillary load was measured by the semi-quantitative method in use in tuberculosis control programmes (i.e. 1+, 2+, 3+) . An admission chest X-ray for each patient was reviewed and interpreted. Each chest radiograph was divided into six zones by eye and the presence or absence of parenchymal disease was recorded for each zone. The presence or absence of cavities was also noted.
A sputum sample was collected from each patient with persistent positive sputum smears after two months of treatment for culture and drug susceptibility testing to the different antituberculosis drugs. Cultures for M. tuberculosis were carried out using the classical Lowenstein-Jensen (LJ) solid medium and susceptibility to different antituberculosis drugs (rifampicin, isoniazid, ethambutol and streptomycin) was based on the standard proportion method. Sputum specimens collected from each eligible patient were decontaminated and inoculated onto LJ. Cultures were incubated at 37°C and read weekly for growth for a maximum duration of 8 weeks. The identification of the cultured strains was based on the following: culture aspects on the two media, resistance to thiophene-2-carboxylic acid hydrazide (TCH, 2 mg/l), susceptibility to para-amino-salicylic acid (PAS, 0.5 mg/l), reduction of nitrates, niacin production and catalase production at 22°C and 68°C. Drug susceptibility testing of M. tuberculosis complex strains isolated from cultures was performed using the indirect proportion method on LJ medium as described by Canetti et al. . A patient was considered to harbour drug-resistant M. tuberculosis if the number of colonies growing on a medium containing 0.2 mg/l INH, 2 mg/l EMB, 4 mg/l SM or 40 mg/l RMP exceeded 1% of the growth on a drug-free culture plate.
All the patients with positive sputum smears at the end of the initial intensive phase of treatment were given an additional month of intensive phase therapy followed by a three month continuation phase of treatment. Sputum smears of each patient were again examined for AFB at the end of the fifth and sixth month of treatment. Outcomes of treatment were then recorded accordingly at the end of six months of therapy. The study was approved by the administrative authorities of the YJH and Cameroon National Ethics Committee.
Data were analysed with the use of the SPSS® statistical software version 17 (SPSS Inc., Chicago, USA). Chi square and Fisher’s exact tests were used to compare proportions, and Mann–Whitney U test was used to compare quantitative variables in both groups. Logistic regression analysis was used to determine the baseline factors associated with culture non-conversion at the end of the second month of intensive phase of antituberculosis therapy. Potential candidate predictors were first investigated in univariate analysis and significant variables (based on a threshold probability of 0.1) were all entered in the same multivariable logistic model to determine independent predictors for culture non-conversion in patients with persistent sputum smear positivity after two months of intensive therapy. A p-value <0.05 was used to characterize significant results.