Setting and study participants
Administratively, Ethiopia is divided into 9 regional states and two City administrations. Each administrative Region is divided into several Zones and each Zone is divided into several Woredas (the third level administrative divisions). The health service delivery system also follows the political administrative structure. Each Woreda has health centers in such a way that 25,000 people are served in one health center.
Data collection for the current study was done between November 2011 and March 2012. A cross-sectional study design was used to recruit patients with cough of any duration at the outpatient clinics of four health centers in Shashogo Woreda, Hadiya Zone, Southern Nations, Nationalities, and Peoples' Region of Ethiopia. The administrative Capital of Hadiya Zone is Hosanna and there are five health centers in Shashogo Woreda. The four health centers included for patient recruitment are Bonosha, Jemaya, Hirko & Shemo. The fifth health center was excluded from the current study since it was not providing smear microscopy service during the study period.
Sample size required in each group of patients (i.e. patients with cough lasting less than 2 weeks and patients with cough lasting for at least two weeks) was estimated using a method appropraite to estimate a single population proportion . We assumed a 14.6% prevalence of smear positive PTB among patients with cough of two weeks  and 7.1% prevalence (i.e. half the prevalence among those with cough lasting at least 2 weeks) of smear positive PTB among patients with cough less than two weeks, 4% margin of error in the estimates in each group and 95% confidence level. With these assumptions, the required sample sizes were 299 for those with cough lasting two or more weeks and 162 for those with cough lasting less than two weeks. Hence, a total of 461 patients presenting to the outpatient clinic of the target health centers with cough of any duration were included in this study.
Data collection, smear microscopy and quality control
Before data collection, health workers who have been working at the outpatient departments of the four health centers were trained. The health workers registered patients aged five years and above with cough of any duration and requested patients to submit three sputum samples as per the national guidelines . Data on patients’ marital status, occupation, education, duration of cough in days or weeks and sputum results were collected. One focal person from each health center out-patient case team was given responsibility of coordinating data collection. Since the standard procedure for diagnosis of pulmonary tuberculosis in Ethiopia is through passive case finding, where all patients with cough for two or more weeks are required to submit three sputum samples in the form of “spot-morning-spot” , the same procedure was used in this study. Training was given to all laboratory personnel from the four health centers to harmonize smear microscopy procedures. The quality check for the submitted samples was done according to the national guideline . External quality assessment as well as on-site evaluation of methods and procedures was done at each peripheral health facility laboratory level. During the study period, Hossana sub-regional laboratory conducted quality assurance as part of its routine external quality assessment. All positive and some negative slides were re-checked blindly (blinded re-checking) for quality control and the results were satisfactory as confirmed by the sub-regional laboratory.
Besides, to evaluate the trends of smear positive pulmonary TB and to compare the result with the current prevalence, we extracted secondary data from laboratory registration books of each health center covering a period of six years.
Data was computerized using EpiData version 3.1 and data analysis was performed using Stata version 11. The proportion of patients with smear positive PTB was calculated for the two study groups (i.e. according to their cough duration). A possible association between PTB and patients’ background characterstics as well as cough duration was investigated using Pearson’s chi-square. Statistically significant associations were reported whenever p-value was less than 5%.
The study was approved by the Institutional Review Board of Aklillu Lemma Institute of Pathobiology, Addis Ababa University before commencing data collection. Written consent was signed by each participant (guardians for children) before enrolment into the study. All patients with smear positive PTB were referred to the TB clinic for treatment and smear negative patients were treated according to the National Guideline.