Browsing Other Diseases by Journal
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Effectiveness of Incidence Thresholds for Detection and Control of Meningococcal Meningitis Epidemics in Northern Togo.BACKGROUND: Early outbreak detection is necessary for control of meningococcal meningitis epidemics. A weekly incidence of 15 cases per 100 000 inhabitants averaged over 2 consecutive weeks is recommended by the World Health Organization (WHO) for detection of meningitis epidemics in Africa. This and other thresholds are tested for ability to predict outbreaks and timeliness for control measures. METHODS: Meningitis cases recorded for 1990-1997 in health centres of northern Togo were reviewed. Weekly and annual incidences were determined for each district. Ability of different weekly incidence thresholds to detect outbreaks was assessed according to sensitivity, specificity, and positive and negative predictive values. The number of cases potentially prevented by reactive vaccination in 1997 was calculated for each threshold. RESULTS: Outbreaks occurred in 1995-1996 and in 1996-1997. The WHO-recommended threshold had good specificity but low sensitivity. Thresholds of 10 and 7 cases per 100,000 inhabitants in one week had sensitivity and specificity of 100% and increased the time available for intervention by more than one or two weeks, respectively. A maximum of 65% of cases could have been prevented during the 1997 epidemic, with up to 8% fewer cases prevented for each week of delay in achieving vaccine coverage. CONCLUSIONS: In northern Togo, thresholds of 7 or 10 cases per 100,000 inhabitants per week were excellent predictors of meningitis epidemics and allowed more time for a reactive vaccination strategy than current recommendations.
Estimates of measles case fatality ratios: a comprehensive review of community-based studies.BACKGROUND: Global deaths from measles have decreased notably in past decades, due to both increases in immunization rates and decreases in measles case fatality ratios (CFRs). While some aspects of the reduction in measles mortality can be monitored through increases in immunization coverage, estimating the level of measles deaths (in absolute terms) is problematic, particularly since incidence-based methods of estimation rely on accurate measures of measles CFRs. These ratios vary widely by geographic and epidemiologic context and even within the same community from year-to-year. METHODS: To understand better the variations in CFRs, we reviewed community-based studies published between 1980 and 2008 reporting age-specific measles CFRs. RESULTS: The results of the search consistently document that measles CFRs are highest in unvaccinated children under age 5 years; in outbreaks; the lowest CFRs occur in vaccinated children regardless of setting. The broad range of case and death definitions, study populations and geography highlight the complexities in extrapolating results for global public health planning. CONCLUSIONS: Values for measles CFRs remain imprecise, resulting in continued uncertainty about the actual toll measles exacts.
Measles outbreaks in the Mozambican refugee camps in Malawi: the continued need for an effective vaccine.Between November 1988 and January 1989, measles outbreaks occurred in 11 Mozambican refugee camps in Malawi with five camps principally affected. A total of 1214 cases were reported. Despite the reduction of the age of measles vaccination to six months in 1987, attack rates were highest in children aged 6-9 months (10-26%); rates were also high in the 0-5 month age group (3-21%). The case-fatality rate was high among children less than five years old (15-21%). Children were being inappropriately vaccinated, either being vaccinated at less than six months of age (2-29%) or failing to receive a second dose if vaccinated at six months (0-25%). With vaccine coverage between 66-87%, vaccine efficacy in children less than five years old was estimated to be more than 90% in the camps principally affected. Reduction of the age of vaccination leads to logistical problems in vaccine delivery in refugee situations. These outbreaks again indicate the need to improve vaccine coverage with the existing Schwarz vaccine, and also highlight the urgent need for an effective single dose measles vaccine for children less than nine months of age.