Study setting and study design

An unmatched case–control study was conducted from December 28, 2016, to January 30, 2017, in public health facilities located in Worabe town, Silte zone, Southern Nation Nationalities, and People’s Region. Worabe town is the capital town of Silte zone. The town has a total population of 29,600, of which 4618 are under-five children. There are two public health facilities in Worabe town and 6 private clinics38.

Study population

Children who were 2–59 months old, and those who visited the selected health facilities during the study period.

Cases were children aged 2–59 months who visited pediatric units, registered and diagnosed with pneumonia as defined by the Federal Democratic Republic of Ethiopian Ministry of Health Integrated Management of Childhood Illness (IMNCI) guideline that is adapted from WHO39.

The control group was defined as children aged 2–59 months without pneumonia and attended the public health facilities in Worabe town.

Sample size determination and sampling technique

A sample size of 435(145 cases and 290 controls) was determined using Epi-Info version 3.5.4 statistical software assumingtwo side confidence level (Cl) of 95%, power = 80%, ratio control to case 2:1, and taking a history of AURTI as a predictor of pneumonia with 22.4% prevalence among control group; 1.80 Odds ratio from a case–control study21 and an estimated non-response rate of 10%. All public health facilities in the town were purposively included based on patient load and the presence of accessible trained staff on IMNCI. The sample size was distributed to each health facility based on the average daily caseload. According to the zonal health bureau Health Management Information System report, the average daily pneumonia patients among under-five children at Worabe comprehensive specialized hospital (WCSH) was seven and it was two at Worabe Health Centre40. Based on this, the sample size allocated for the Worabe health centre was one case and two controls on a daily basis with a total of 21 cases and 42 controls. The sample size allocated for WCSH was six cases and twelve controls on a daily basis with a total of 124 cases and 248 controls.

Selection of cases

All cases (diagnosed and recorded as pneumonia/severe pneumonia) were considered in the study until the required sample size was reached/fulfilled.

Selection of controls

As the control-to-case ratio was 2:1, two children who did not have pneumonia and visited selected health facilities for different services at the time of data collection were randomly selected by systematic random sampling after the cases were identified.

Eligibility criteria

The study included children who were between 2 and 59 months of age, those who were residents of Worabe town for a minimum of six months, and visited the pediatric unit of WCSH and Worabe Health Center during the study period.

Children with the following conditions were excluded from the study: cardiac disease, cough that lasted for > 15 days (suspected of pulmonary tuberculosis), cough because of the recent history of aspiration of a liquid or a foreign body, and caregiver who did not have any information about the child at the time of data collection.

Study variables

Dependent variables

Presence of pneumonia.

Independent variables

Socio-demographic factors: Parental factors such as educational and occupational status, parental cigarette smoking, age of the mother, family size, and family caring practice (parental/home maid, place of child during cooking, and family income).

Child factors: age and sex, immunization status, a pre-existing illness such as a history of diarrhoea, AURTI, and acute lower respiratory tract infection/pneumonia in the last 2 weeks and asthma.

Environmental factors: type of fuel used for cooking, crowding status, place of cooking, parental asthma, and household history of tuberculosis and pneumonia.

Nutritional condition of the child: undernutrition, breastfeeding status of the child for the first 6 months and duration of breastfeeding, age of complementary feeding started, and zinc supplementation.

Operational definitions


A child aged 2–59 months with cough and/or difficulty in breathing for less than two weeks of duration plus fast breathing and/or chest in drawing15,16,17,18,19.

Fast breathing is defined as:

  • For children in the age interval of 2–11 months, 50 breaths per minute or more

  • For children in the age interval of 12 months to 5 years, 40 breaths per minute or more39,40,41.

History of acute upper respiratory tract infection(AURTI): a child who had a history of ear infection, common cold, tonsillitis, or pharyngitis in the last fifteen days prior to data collection42.

Underweight: Weight at the birth of less than 2500 g43,44.

Stunting: Chronic undernutrition condition in which a child is short for his or her age44.

Wasting: Unintended loss of weight which makes children too thin and weak45.

Data collection tools and procedures

A structured questionnaire was developed based on a review of previously published studies and adapted for the current study with certain modifications17,18,19,20,21,22,23,24,25,26,27,28. The questionnaires included information on the possible risk factors for pneumonia, including socio-demographic factors, environmental/home-based factors, nutritional factors, immunization status, pre-existing illness and child care practices. Data were collected by IMNCI-trained nurses working in under-five clinics who received two days of training regarding the research. After the study participants were identified as cases and controls, mothers/primary caretakers were interviewed based on the interviewer-administered pretested structured questionnaire.

Anthropometric measurements

The weight and height of the child were taken at the beginning of the interview by data collectors. A suspended scale of 25 kg capacity graduated at 0.1 kg was used for weighing infants and children. The reading was recorded to the nearest 0.1 kg. Length measurements in the lying position were taken for children less than two years of age, and height measurements were taken for children 2–5 years of age. The anthropometric data were analysed in terms of weight for age, length for age, and weight for length using WHO Anthrosoftware to prepare for SPSS. The WHO (2006) growth standard was used to report anthropometric measurements result by Z-score, and the global acute malnutrition standard was used to classify the child’s nutritional status as normal, stunted, wasted, or underweight.

Data quality management

The questionnaire was pretested on a 5% sample size at Kbit Primary Hospital to ensure the validity and reliability of the survey tools. After collecting the pre-test data, it was checked for potential problems related to the tool, such as any difficult question that was understandable or unclear to reply and corrective measures were taken.

Data processing and analysis

The collected data were checked for completeness, coded and entered into Epi Info version 7 and exported to the statistical package for social sciences (SPSS) version 22 for analysis. The entered data were cleaned and checked for consistency and extent of outliers. Different statistical assumptions and appropriate corrections were made prior to analysis. Descriptive analyses were carried out for each of the independent variables. Bivariable and multivariable binary logistic regression analysis was used to test the association between the independent and dependent variables. Bivariable analysis was performed for each of the independent variables with the outcome variable. Variables that had a p-value < 0.2 on bivariate analysis were taken as candidates for multivariable binary logistic regression model analysis to identify predictors of the outcome variables. Variables with a p-value less than 0.05 on multivariable logistic regression analysis were considered statically significant factors for the outcome variables. The strength of the association between the dependent variable and independent variables was expressed using adjusted odds ratio (AOR) with 95% confidence intervals.

Ethical approval and consent to participant

The study was ethically approved by the Institutional Review Board of Saint Paul’s Millennium Medical College Department of Public Health. An official permission letter was obtained from the study site. The objectives, expected outcomes, benefits, and risks of the study were explained to mothers/guardians/caregivers of the study participants. Data were collected after written informed consent was obtained. The study was conducted in accordance with the Declaration of Helsinki.

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