Time Series Analysis of Cholera in Guinea-Bissau, 1996-2008
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TIME SERIES ANALYSIS OF CHOLERA IN GUINEA-BISSAU, 1996-2008. Report v. 2.0 December 2009 Francisco J. Luquero WHO Collaborating Centre for Epidemiology Research and Response to Emerging Diseases TELEPHONE: 00 33 (0)1 40 21 55 55 FAX: 00 33 (0)1 40 21 28 03 E-MAIL: [email protected] ACKNOWLEDGEMENTS This study was carried out in close collaboration with the Instituto Nacional de Saude and the World Health Organization. In particular, Dr. Agustinho Betumde and Dr. Cesario Martins from INASA, and the Dr. Alvarenga, head of the Preparedness and Response Unit of the WHO country office were close partners in this study. We want also thank the support to the UNICEF team, especially to Suzana Alfama and François Enten. I also wish to acknowledge Rebecca Grais and Biagio Pedalino for their comments and suggestions. The source of financial support for this study was provided by the United Nations Children's Emergency Fund (UNICEF), USAID and the European Commission for Humanitarian Aid (ECHO). We declare that we have no conflict of interest. 2 Abbreviations AR Attack Rate BHS Basic Health Structure CFR Case Fatality Ratio CTC Cholera Treatment Center CTU Cholera Treatment Unit CHU Community Health Units CHW Community Health Worker DGS Public Health General Direction ECHO European Commission Humanitarian Aid HBU Health Base Units INASA Instituto Nacional de Saúde LNSP National Public Health Laboratory MPH Ministry of Public Health MSF Médecins Sans Frontières MSF-OCBA Medicos Sin Fronteras- Spanish section NGO Non-governmental organization RDH Regional Direction of Heal SAB Sector Autonomo de Bissau SA Sanitary Area UNICEF The United Nations Children's Fund WHO World Health Organization WHS Water, Hygiene and Sanitation 3 Table of contents 1 Background.................................................................................................................................... 5 1.1 Clinical features ............................................................................................................................................7 1.2 Epidemiology ................................................................................................................................................7 1.3 Cholera in Guinea-Bissau.............................................................................................................................8 1.4 Rationale.......................................................................................................................................................8 1.5 Objectives .....................................................................................................................................................9 2 Materials and methods ................................................................................................................ 10 2.1 The cholera surveillance system in Guinea-Bissau ....................................................................................10 2.2 Case definition ............................................................................................................................................10 2.3 Cholera data base.......................................................................................................................................10 2.4 Time series analysis ...................................................................................................................................11 2.4.1 Description of historical data..................................................................................................................11 2.4.2 Seasonal risk analysis ...........................................................................................................................11 2.4.3 Threshold to define outbreaks with potential to produce large epidemics..............................................12 2.5 Ethical considerations.................................................................................................................................12 3 Results.......................................................................................................................................... 13 3.1 Historical cholera epidemics in Guinea-Bissau from 1996 to 2008.............................................................13 3.1.1 1996-1997 epidemic ..............................................................................................................................13 3.1.2 2004 epidemic........................................................................................................................................19 3.1.3 2005 epidemic........................................................................................................................................21 3.1.4 2007 epidemic........................................................................................................................................25 3.1.5 2008 epidemic........................................................................................................................................27 3.2 Predictive model of the seasonal risk of cholera in Guinea-Bissau ............................................................32 3.2.1 Risk model for Guinea-Bissau................................................................................................................33 3.2.2 Risk model for Bissau-Sector.................................................................................................................34 3.2.3 Risk model for Biombo region................................................................................................................35 3.2.4 Risk model for Bijagos Islands...............................................................................................................36 3.3 Decision framework to define situations with high epidemic potential. .......................................................37 3.3.1 Spatial differences in the first 60 days of epidemic................................................................................37 3.3.2 Time differences in the first 60 days of the epidemic.............................................................................38 3.3.3 Decision framework ...............................................................................................................................39 4 Discussion.................................................................................................................................... 41 5 Conclusion and recommendations ............................................................................................ 43 5.1 Conclusion ..................................................................................................................................................43 5.2 Recommendations......................................................................................................................................43 6 ANNEX .......................................................................................................................................... 45 6.1 Evolution of the 1996-1998 epidemic..........................................................................................................45 6.2 Evolution of the 2005 epidemic...................................................................................................................45 6.3 Evolution of the 2008 epidemic...................................................................................................................45 6.4 Annex 4: Global overview of the 1996-2008 period ....................................................................................46 4 Index of tables and figures Table 1. Cholera cases, deaths, attack rates and fatality by region. Guinea-Bissau. 1996-1998.......................... 17 Table 2. Cholera cases, deaths, attack rates and fatality by region. Guinea-Bissau. 2004................................... 21 Table 3. Cholera cases, deaths, attack rates and fatality by region. Guinea-Bissau. 2005................................... 23 Table 4. Cholera cases, deaths, attack rates and fatality by region. Guinea-Bissau. 2007................................... 26 Table 5. Cholera cases, deaths, attack rates and fatality by region. Guinea-Bissau. 2008................................... 29 Table 6. Number of cases, population, attack rate per 100 people at risk (AR %), risk ratio (RR) and adjusted risk ratio (ARR) by Sanitary Area, age and gender in SAB until 20/10/2008................................................................ 31 Figure 1. Number of cholera cases notified to the World Health Organization (WHO) in Guinea-Bissau. 1994- 2008. Source: WHO weekly epidemiological report. ............................................................................................... 8 Figure 2. Daily number of cholera cases in Guinea-Bissau. October 1996 to April 1997...................................... 13 Figure 3. Weekly number of cholera cases in Guinea-Bissau. January 1996 to April 1997. ................................. 14 Figure 4. Cholera attack rates by sanitary area in Guinea-Bissau. October 1996 to April 1997............................ 14 Figure 5. Daily number of cholera cases in Bissau and Biombo regions. January 1996 to April 1997.................. 15 Figure 10. Daily number of cholera cases in São Domingos, Nhacra and Bedanda regions. May 1997 to January 1998 .....................................................................................................................................................................