2009 in Harare, Zimbabwe: a Secondary Data Analysis
Total Page:16
File Type:pdf, Size:1020Kb
Transactions of the Royal Society of Tropical Medicine and Hygiene 105 (2011) 38–45 Contents lists available at ScienceDirect Transactions of the Royal Society of Tropical Medicine and Hygiene journal homepage: http://www.elsevier.com/locate/trstmh Descriptive spatial analysis of the cholera epidemic 2008–2009 in Harare, Zimbabwe: a secondary data analysis Miguel Ángel Luque Fernández a,∗, Peter R. Mason b, Henry Gray c, Ariane Bauernfeind a, Downloaded from Jean Franc¸ois Fesselet d, Peter Maes c a Médecins Sans Frontières, Medical department (Brussels Operational Center), 94, rue Dupre, 1090 Brussels, Belgium b Biomedical Research and Training Institute, University of Zimbabwe College of Health Sciences, Harare, Zimbabwe c Médecins Sans Frontières, Medical Department, Water, Hygiene and Sanitation Unit, Brussels Operational Centre, Belgium d Médecins Sans Frontières, Public health department, Water, Hygiene and Sanitation Unit, Amsterdam Operational Centre, Holland http://trstmh.oxfordjournals.org/ article info abstract Article history: This ecological study describes the cholera epidemic in Harare during 2008-2009 and iden- Received 15 April 2010 tifies patterns that may explain transmission. Rates ratios of cholera cases by suburb were Received in revised form 1 October 2010 calculated by a univariate regression Poisson model and then, through an Empirical Bayes Accepted 1 October 2010 modelling, smoothed rate ratios were estimated and represented geographically. Mbare Available online 13 November 2010 and southwest suburbs of Harare presented higher rate ratios. Suburbs attack rates ranged from 1.2 (95% Cl = 0.7–1.6) cases per 1000 people in Tynwald to 90.3 (95% Cl = 82.8–98.2) Keywords: in Hopley. The identification of this spatial pattern in the spread, characterised by low risk Cholera at University of Arizona on May 10, 2016 Disease Outbreaks in low density residential housing, and a higher risk in high density south west suburbs Epidemiology and Mbare, could be used to advocate for improving water and sanitation conditions and Zimbabwe specific preparedness measures in the most affected areas. Africa © 2010 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved. 1. Introduction half of which occurred in the urban centres of Harare and Chitungwiza.2–7 On 20 August 2008 an outbreak of 118 cholera cases During the 2008–2009 Zimbabwe cholera epidemic the was declared in St. Mary’s and Zengeza wards of Chitung- country was in economic crisis and the health care system wiza, a large urban centre on the outskirts of Harare.1–5 had become dysfunctional, with most government hospi- Vibrio cholerae El Tor 01 was isolated from 18 (30%) of tals unable to provide services or closed due to a lack of the 59 specimens collected, thus supporting the clinical essential medical supplies. Many staff in health structures evidence for an outbreak.2 Two months after this initial had not been paid, and many were unable to report for duty. outbreak, a second wave of cases was reported with numer- Water supplies were irregular and sanitation systems had ous suburbs being affected within the city of Harare and collapsed. The reason for this was a lack of maintenance within every province of the country. This was the largest of the system, with frequent power interruptions affecting and most extensive outbreak of cholera recorded in Zim- pumping stations.8–11 babwe and indeed in Africa, affecting rural and urban areas By 2008, Chitungwiza had been without adequate water with more than 100 000 cases and 4000 deaths, about supply water for more than two years. People had become dependent on shallow wells that were at risk of contam- ination because of the lack of sewage disposal.1,9,11 On 1 ∗ December 2008, problems with the main pumping sta- Corresponding author. E-mail addresses: [email protected], tion meant that, without prior warning, the water supply [email protected] (M.Á. Luque Fernández). was shut off for Harare, leaving large populations without 0035-9203/$ – see front matter © 2010 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.trstmh.2010.10.001 M.Á. Luque Fernández et al. / Transactions of the Royal Society of Tropical Medicine and Hygiene 105 (2011) 38–45 39 Table 1 In line with the above it can be hypothesised that the Distribution of cholera cases by sex and age in the treatment centres dur- distribution of cholera cases by suburb in Harare during ing the cholera outbreak in Harare, 2008–2009 (n=19 422 cholera cases) the epidemic of 2008-2009 followed an identifiable spatial Variables n (%) pattern related to the active population movements and Sex high density population areas. Males 10 071 (51.9) There are currently no published data showing the spa- Females 9272 (47.7) tial distribution and spread of cholera cases in Harare. Data missing 79 (0.4) In this paper we describe the spatial distribution of the Age in years cholera epidemic in Harare and Chitungwiza and identify ≤5 3542 (18.2) factors that influenced the spatial pattern of the outbreak 6-14 1932 (9.9) spread that may explain mechanism of transmission, in 15-24 3811 (19.6) 25-34 4828 (24.9) order to guide future preparedness and control measures. 35-44 2682 (13.8) ≥45 2627 (13.5) 2. Methods Children ≤5 years 0-2 2356 (66.5) We developed a population-based ecological study 3-5 1186 (33.5) using a secondary data analysis. The study protocol was Downloaded from approved by the Ethical Review Board of Médecins Sans access to potable water. With no water supply, the lim- Frontières (MSF). ited health structures that continued to operate could not Data were drawn from the register of cholera treatment maintain an acceptable level of infection control and many centres (CTCs) and oral rehydration points (ORPs) function- ing during the cholera epidemic in Harare and Chitungwiza. hospitals were closed.10 http://trstmh.oxfordjournals.org/ The city of Harare is characterised by lower density MSF, in collaboration with the Department of City Health affluent suburbs in the north and high density poorer areas of the Ministry of Health and Child Welfare, implemented in the south.12 Chitungwiza is a high density dormitory city and managed three CTCs, in Budiriro Polyclinic, the Beat- in the south of Harare, which was established mainly to rice Road Infectious Diseases Hospital and in Chitungwiza. house workers commuting daily to Harare. The main form Ten ORPs were functioning in Harare city and one in Chi- of transport in Harare and Chitungwiza is the minibus, a tungwiza. privately-owned small bus that collects passengers from Population figures by suburb were calculated from the designated bus stops. official census of Harare and Chitungwiza, completed in Also in Harare and Chitungwiza a large proportion of 2002. To estimate the populations’ figures at the time of the economic activity is concentrated at informal markets. epidemic we employed an average constant annual growth at University of Arizona on May 10, 2016 Markets are particularly common in high density sub- rate of 3%, as estimated by the Population Division of the urbs where they serve the needs of commuters. In the Department of Economic and Social Affairs of the United 17 past, city regulations restricted market trading, particu- Nations Secretariat. larly of food products, to sites with appropriate water and For the case definition of cholera, we used the definition sanitation facilities. At the time of the cholera outbreak, as listed in the MSF cholera guidelines: in an area where however, implementation of this regulatory framework there is a cholera epidemic a cholera case is defined as had already broken down, and most trading was at infor- any patient presenting three or more liquid stools and/or 18 mal sites with limited or no access to clean water.12,13 vomiting for the last 24 hours. In disadvantaged settings Vibrio cholerae is predominantly In the statistical analysis we describe the outbreak in 19–21 transmitted by contaminated water and through person to the classical way, in terms of person, place and time. person contact,14,15 and the risk of transmission is greatest We calculated descriptive statistics for the variables related in overcrowded areas, including markets. Markets selling to person (age, sex). To describe the outbreak by place food items, particularly those that lack sanitation or access we calculated the attack rates for each suburb, including to clean water, may facilitate the spread of diarrheal disease 95% exact confidence intervals (Cl) under the assumption 22 agents.16 that the attack rates follow a Poisson distribution. Then, to describe epidemic time evolution, we presented epi- demic curves for suburbs with more than fifty cholera Table 2 cases. Age of cholera cases by sex in the treatment centres during the cholera out- break in Harare, 2008–2009 (n=19 343 cholera cases, 72 missing values In order to describe the relation between the cholera of sex variable, listwise analyse) cases and high density population areas, we computed the Pearson’s correlation coefficient (R) between the number Male, n (%) Female, n (%) P-valuea of cholera cases and the number of bus stops plus mar- Age by sex <0.001 kets by suburbs. Then, we represented a scatter plot, taking ≤5 1955 (19.4) 1566 (16.9) out extreme values, to show the relation between cholera 5-14 1041 (10.3) 879 (9.5) 15-24 1672 (16.6) 2126 (22.9) cases and the number of bus stops plus markets by sub- 25-34 2486 (24.7) 2328 (25.1) urbs. Both variables were drawn from the Department 35-44 1587 (15.8) 1088 (11.7) of the Surveyor-General of the government of Zimbabwe, ≥ 45 1330 (13.2) 1285 (13.9) and have been used as proxies of overcrowded and high a 2 Pearson 5df = 177.3 mobility areas, where the probability of person to person 40 M.Á.