Study design, period and setting
A community based cross-sectional study design was used. Fieldwork was undertaken from March 11, 2017 to April 26, 2107. The estimated population of Wadla district was 128,170 with 64,574 males and 63,596 females. There were 28,414 households in this district with an average of 4.51 persons per house. The district had 1 general hospital, 7 health centers, and 20 health posts.
The sampling frame was children aged 1–5 years and their mothers in 150 rural villages of Wadla district. The study units were rural households that had preschool-age children.
Sample size determination
We estimated the required sample size using the single population proportion formula.We assumed, based on previous surveys, an observed prevalence of active trachoma (12.1%) (16), which we wished to estimate with 95% confidence within ±5%. We used a design effect of 1.5, and allowed for 10% non- response rate. Then, the sample calculated as follow
See formula 1 in the supplementary files.
Where Z is the 95% CI, d is marigion of error, p is the observed prevalence of active trachoma, and q is the observed trachoma free prevalence, and n is the required sample size.
n = (1.96)2 (0.121 × 0.879),
n = 3.8416 ×0.106359 = 163.435 ≈ 163
After multiplying by the design effect of 1.5 and incorporating a 10% non-response rate, we estimated that (163 ×1.5), 244.5+24.45=268.9 ≈ 269 children needed to be framed in selected households.
Sampling technique and procedure
A multistage cluster sampling technique was applied. Wadla district had 20 Kebeles (sub-districts) with 247 villages. Twelve of the kebeles were rural, whereas eight of the kebeles were urban. This meant that 150 of the 247 villages were rural.We used simple random sampling to select 30 villages. There were 967 households in the selected 30 villages, but only 499 of those households had preschool children. Those 499 households were visited. Heads of households were interviewed for socio-demographic and economic information, plus housing and environmental conditions, and all children aged between 1 and 5 years who had been resident in the district for at least six months were invited to be examined. Graders used the WHO simplified trachoma grading scheme to grade signs of trachoma (17) (Figure1).
Clean face: A child free of eye discharges, nose discharges and flies on the face at the time of examination
Preschool: Children aged greater than and equal to 1 year and less than or equal to five years
Village: A grouping of homes that contained at least 30 households that organized as one peasant association
Active trachoma: Preschool children who had at least one of the two signs of active trachoma in the WHO simplified trachoma grading scheme (TF or TI) in eye (4, 18, 19).
Trachomatous inflammation follicular (TF): Five or more follicles each having a diameter of at least 0.5mm in the central part of the upper tarsal conjunctiva(4, 18, 19).
Trachomatous inflammation—intense (TI): a pronounced inflammatory thickening of the upper tarsal conjunctiva that obscures more than half of the normal deep tarsal blood vessels (4, 18, 19).
Trachomatous scarring (TS): easily visible scarring in the upper tarsal conjunctiva (4, 18, 19)
Trachomatous trichiasis (TT): at least one eyelash rubs on the eyeball, or evidence of removal of inturned eyelashes in the two weeks before examination (4, 18, 19).
Corneal opacity (CO): easily visible corneal opacity over the pupil (2, 6, 20)
Exclusion and Inclusion Criteria
All children in the appropriate age range who had lived in the district for at least 6 months, who were resident in selected villages and available at the time of the study were invited to be included. Children who were seriously ill or for whom informed consent for participationwas withheld by parents or guardians were excluded
Data collection tools and procedures
Face to face interviews, observation using a checklist, and clinical eye examination were used. Socio-demographic status, environmental, and housing conditions were collected by experienced health informatics professionals using structured interview questions, which were prepared following a literature review (21, 22). All questionaries on socio-demographic status, housing, and environmental condition, observation checklist, and eye examination tools were pretested, and validated before data collection in Kosomender, Meket district, a district bordering Wadla to the north. A household wealth index was developed using composite indicators for rural residents’assets: livestock ownership, size of agricultural land and quantity of crop production.
Two integrated eye care workers performed eye examination: Those integrated eye care workers are ophthalmic nurses, who had been trained for one month for the purpose of national trachoma survey by the Carter Center-Ethiopia. Carter Center delivered the training using both pictures and live patients as media of instruction. Thus, we were selecting trachoma graders who had an experience of nationa trachoma survey under the control and supervision of Carter Center-Ethiopia. Fortunatly, both of the graders had been involved in two previous national trachoma surveys as trachoma graders. However, the scope, objective, data collection methods, and study population of our study was differe from nationa trachoma survey. For this reason, the trachoma graders took refreshment training for 5 days. The training also delivered for interviwers. Those interviewers assist the graders by recording the type of trachoma identified, and other data related to the houshold’s socio-demographic status, housing, and environmental situations. The training emphasized the objectives and procedures of the data collection and mode of communication between graders and interviewers. Specifically, graders provided with an additional 58 live patients and 100 pictures of different trachoma signs independently. Trainers’ grades were used as the gold-standard assessment, when neither grader disagreed with trainers’ grades on any picture or live subject. When undertaking the actual field work for the study, graders initially observed the eyelashes and cornea of study subjects, looking for TT and CO, then everted the upper lid and inspected the upper tarsal conjunctiva for TF, TI and TS. Binocular lenses (×2.5) and penlight torches were used (4) to magnifiy the examined eye.
Data analysis and presentation
Data were checked for completeness, coded, and entered into Epi-info version 7, and then transferred to SPSS version 23 for analysis. Data were checked for normality using Hosmer-Lemeshow-goodness-of-fit. A univariable analysis model were carried out; and variables that had p-value <0.25 in binary logistic regression model were included in the multivary logistic regression model analysis. Potential co-linearity was also considered and tested using multi co-linearity in considering tolerance and variance infletion factor (VIF).Variables with a p-value < 0.05 in multivary logistic regression analysis were considered statistically significant. A principal components analysis was performed to categorize households’ wealth into poorer, poorest, middle, richer, and richest. However, for the presentation of the variables, the wealth index was recoded in to three groups; lowest, middle, and highest. Both active trachoma and cicatricial trachoma were modelled as outcome variables (Figure 2).
Data Quality Assurance
The questionnaire was prepared in English and translated to Amharic, then back translated to English to allow a check for accuracy by individuals fluent in both English and Amharic. Both graders and one of the researchers participated previously in a community-based trachoma survey. The interviewers also had previous experience in community-based data collection. The inter-rater variability of eye examination assessed by enlisting certified trachoma graders, who had certified by Carter center-Ethiopia, and had participated in two national trachoma surveys. A refreshing training was delivered for both graders by the principal investigators and one ophthalmologist for five days. On the third day of the training, all the teams went to the field to undertake and practice eye examinations on rural preschool children. Results of examinations of those 58 children were discussed during the fourth and fifth days of the training.