Prevalence of hypertension and its risk factors in Western area urban, Freetown Sierra Leone: a hospital-based survey

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Thesis on Hypertension

Methodology

Introduction

This chapter covers the methods used to understand the prevalence and risk factors of hypertension in Western Area District of Sierra Leone. It discusses the study design, Study period,study region, study setting, sample size calculation,validation, data analysis, etc.Thedata collection instrument used to collect dataand statistical methods used to calculate the relationship between risk factors and hypertension, reliability, and challenges that were in this studyare discussed too.

Study approach and design

This study was a cross-sectional descriptive hospital-based survey conducted at the outpatient departments in three hospitals in Western urban, Freetown, Sierra Leone.

Study Period
The study was conducted from 15th September 2018 to February 16th, 2019 and data was collected from 1st November 2018 to 1st December 2018.

Study Region
Sierra Leone is in theWest Africanregion of Africa. It shares borders with Guinea to the north and east, Liberia to the south and the Atlantic Ocean to the west. Sierra Leone had suffered from a devastating eleven years civil war between 1990-2002, Ebola epidemic in 2014-2016, killing 3,956 cases out of 14,124 cases as reported by World health organization situation report 27th March 2016, and mudslides in 2017, killing over 10000 people.

Additionally, Sierra Leone has a fragile public health sector which, however, deliver services based on out of pocket expenditure; excluding pregnant women, under-five children, lactating mothers and Ebola survivors under the provision of Sierra Leone parliamentary free healthcare policy.

Research settings
This study was conducted in the western urban region which is one of the two districts making the capital city of Freetown Sierra Leone. These zones have a total of 110 functional primary healthcare, stratified into three peripheral health units(PHU) such as community health centers(CHC), community health post(CHP) and maternal child health post(MCHP) which are managed by different healthcare professionals; 9 secondary hospitals of which 5 is a public sector, managed by medical doctors and 4 tertiary level hospitals, managed by specialist which are categories into pediatrics, obstetrics, and gynecology, mental health and internal medicine and surgery hospitals (Statistics Sierra Leone, 2016 pp.13-16).

This study was conducted in three governmental secondary hospitals which areMacaulay hospital, Rokuprr hospital(MKP), and Lumley hospital(LKP). These hospitals have about 64% residents in the catchment zones. This was made up of 61,244 in MKP, 188,576 in the LKP and 448,572 in RKP(Census,2015)

Target and Study Population
The target population includes all out-patient attending these hospitals from the ages of 20 to 65 years and the study population is those aged from 20-65 who attended the hospital during the data collection period.

Inclusion criteria
All adults between the ages of 20-65 years attending the OPD and resident living within the hospital's catchment zones were selected for this study.

Exclusion criteria
All adults with ambulatory sickness including head injuries, pregnant women and those living outside the hospital catchment zone, were excluded from the study

Sample size
The sample size of 573was calculated using EpiInfo 7.2 Stat calcfound at www.cdc.gov/epiinfo. The nationalpopulation census data for the 3 zones was usedto estimate theappropriate sample size for this study based on the following assumptions:
• The total population size of the three hospitals catchment areas was 699,647 in the selected zones
• The expected proportion of the present prevalence of hypertension was 46% (Award et al.,2014)
• An acceptable margin of error is 5%
• Design effect is 1.5 and
• Clusters are 3

Sampling and recruitment of Participants
Number of participants recruited from a hospital = (the catchment population of that hospital/ Total catchment population of the three hospitals) × 573

Table 1: Number of participants recruited from each of the three hospitals

In the second stage, we used a systematicsampling technique to select study participants at each of the three hospitals. We estimated an attendance of hospital catchment people to be attendance monthly is as follows, Rokuprr4,000, Macauley 1000 and Lumley 1000. To select the first participant for each of the sites using a systematic sample frame and to registerasparticipants to be recruited from each of the sites, the number of catchment population of the hospitals were considered. The sample frame is simply the population of the hospitals who serves as a sample and here the specific number of participants(table above) serves the purpose. A lottery method was conducted to select the first participant for each hospitaland the subsequent participants were recruited based on the intervals calculated to achieve the targeted sample size for the three hospitals.

Data collection instrument
Data were collected using a modified and adapted questionnaire based on the WHOSTEPwise approach and Center for Disease Control and Prevention(CDC) Behavioral Risk Factors Surveillance System(BRFSS). A questionnaire including information on socio-demographic characteristics, behavioral factors, diets, and other chronic diseases and risk factors was developed along with weight and height, blood pressure was collected according to Whelton and colleagues.

The materials used for data collection were: Structured predesigned questionnaire paper, automated blood pressure device, electronic pre-calibrated weighting scale, measuring tape, and pictorial leaflet of the type of tobacco products, alcohol, fruits and vegetables, physical activity and scanned copy of historical events for the last 40 years to determine participants ages.

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Pre-test
Study variables

Table 2: Study variables

Data Collection

The total time of the interviews, including anthropometric measurement and blood pressure, was between 15-30 minutes interval.
Two data collectors were trained and supervised on the study protocol to support the process including recruitment of participants, informed consent, administer face-face interview techniques, measurement of blood pressure and other data collection processes for compliance of the study protocol in the field.

For the study, the lifestyles of the subjects were considered to help in the accuracy level along with the gender and age of a person. The measurements of the subjects like height and weight are crucial proper data collection as these physical properties defines a person as fit or unfit.Hypertension is affected hugely by the weight and height of an individual.

Measurement of BP
Hypertension was defined as a BP reading of 130/80 mm Hg or higher using the new 2017 hypertension Guideline for adults (Wheltonet al., 2017) or self-reported participants patients on hypertensive medications. BP was measured using Omron automated blood pressure machine (Model BP785N and M2 Eco) and automated inflation cuff size (22-32 cm and 22-42 cm) was used to display both SBP and DBP. The automated BP was used to limit other observers around the hospitals. All BP was taken on the right arm after participant rested for at least 5 minutes in a sitting position with their legs uncrossed and right arm free of clothes for the first measurement. The right arm was placed on the table with the palm facing upwards. The appropriate cuff size was selected for, and the artery position mark was aligned with the brachial artery. The cuff was wrapped firmly and secured and was kept at the same level as the heart during measurement. A second reading was taken 5 minutes after the first. The averages of two SBP and DBP measurements were calculated and were used as variables in the analysis.Blood pressure controlled was determined when an average SBP and DBP is less than 130/80 mmHg/and or 80 mmHg for individual taking antihypertensive medication (Wheltonet al., 2017). While poor blood pressure was determined when an average SBP was more or equal to 130 mmHg or an average DBP was equal to 80mmHg in a patient taking the antihypertensive drug. Undiagnosed hypertension was defined as individuals who met Whelton and colleagues (Wheltonet al.,2017).

The study provides the classification of the physical activities, whether high, medium or low, of the participating people as well. The intensity of the physical activities is formulated through the Metabolic Equivalents or METs, which is the ratio of the metabolic rate while resting to the metabolic rate while involved in some activity.

The number days per week on which the activity was carried out was multiplied by the number of minutes taken doing the activity per day and then multiplied by the MET value for each activity to get the number of MET-minutes/week. The number of MET-minutes/week for each activity were then added to get the total number of MET-minute/week which was then used to classify physical activity into high, moderate and low as per WHO STEP guidelines.

BMI was classified according to the proposed criteria of the World Health Organization (WHO) (CED III < 18.5, normal = 18.5-24.5, overweight = 25.0-29.9, and obese ≥30.00.[7] In the present study, all the subjects having BMI ≥30 were taken as obese.

Anthropometric measurement
Body weight was measured to the nearest 0.1kg using a digital personal scale (model: NBS396 in kg made in Japan) with light clothing without shoes and height to the nearest 0.1 cm using a stature meter (model: 2M/220) in a standing position in barefoot with a constant tension tape attached to the wall to reduce inconsistency of the results.

Data processingand analysis
The data was collected from the participants of the four hospitals through a systematic survey and a definite set of questions. The data was collected by trained interviewers and then this data was prepared in a way that would produce efficient answers. The input of the data is done by the officials of the survey in the computer where it is processed to give an output and is stored for future referencing as well.

Table 3: Classification of blood pressure

Table 4: Classification of obesity usingBMI

Source: The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure

The intensity of physical activity was determined based on the Metabolic Equivalents (MET) which implies that the ratio of a person's working metabolic rate relative to the resting metabolic rate.

Data was entered into Epi-info version 7 for processing and analysis. Processed data were checked for completeness and consistency.Descriptive statistics were analyzed such as frequencies, proportions, and means. Prevalence of hypertension was calculated based on the proportion of participants with a measured BP greater than 130/80 mmHg. Bivariate analysis was carried out using cross-tabulations to examine the relationship between the outcomes (hypertension).

Ethical Approval and informed consent
Ethical clearance was obtained from the University of Roehampton Ethics Board in London, England; Sierra Leone Ethics Committee at the Ministry of Health and Sanitation; study site permission consent was sought at the selected hospitals. Verbal and written informed consent was obtained from all the participants after a thorough explanation of the purpose and procedure of the study in Sierra Leonean local dialects. Confidentiality was maintained throughout the study. Individuals incidentally identified of life-threatening blood pressure were urgently referred to the emergency department, and those raised blood pressure were advised to start to follow up for further medical evaluations (Wheltonet al.,2017).

Limitations
The major limitation of this study determined the prevalence of hypertension and its risk factors among hospital outpatient visitors in selected governmental secondary hospitals, instead of private hospitals and primary health care facilities in the communities. Selection bias, those exposed to hypertension risk factors might prefer to access treatment in private hospitals in the community than government hospitals over the study period.

Respondent classified to be hypertensive were based on a single day blood pressure measurement within 5 minutes interval which has the tendency to show false readings without evaluation in the subsequent visits by the researchers as recommended Whelton et.al.2017. Also, a further limitation of this study is the recall bias, as participants do not talk about the use of tobacco products, alcohol consumption, and physical activities.

The respondents for this study drawn in the three hospitals catchment zones were systemically selected based on the estimated population in the various zone as per hospital operation. Thecomplexity and disintegration of the zones as per hospital catchment areas were difficult to identify the resident subject due to lack of enumeration map in each catchment zones.Identification of data was difficult because of the gaps and differences in the test results of the blood pressure tests conducted on the participants. Quantity was also an issue as too much blood collection from a participant for sampling purposes would make him weak. Prioritizing information and participants based on their physicality and extent of Hypertension was hard too but the issues were resolved and a firm statement was formulated.

Criterion validity has used the extent to which a research instrument is related to other instruments that measure the same variables.

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