IDENTIFYING HIGH-RISK AREAS FOR SPORADIC MEASLES OUTBREAKS: LESSONS FROM SOUTH AFRICA.

Monday, 23rd of June 2014

[source]Bulletin of the WHO[|source]

Spatial analysis can be an important epidemiological tool for detecting and predicting patterns of disease spread. In situations where population-wide interventions are too expensive or are inefficient because they dilute available resources, the effectiveness of vaccination is increased by targeting high-risk areas, such as those implicated in measles transmission and those where vaccination coverage varies.

 In this report, the authors investigate the pattern of measles spread in the South African outbreak that occurred between 2009 and 2011. In the investigation, the authors identify associations between the outbreak and population density, HIV prevalence and preceding lapses in measles vaccination. But most importantly, the authors also use their findings to develop a model for identifying areas at a high risk of future large-scale sporadic measles outbreaks that can be used in prevention. More details on the model and how it could be used in your settings are accessible at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3590621/

 

 ABSTRACT

OBJECTIVE: To develop a model for identifying areas at high risk for sporadic measles outbreaks based on an analysis of factors associated with a national outbreak in South Africa between 2009 and 2011.

METHODS: Data on cases occurring before and during the national outbreak were obtained from the South African measles surveillance programme, and data on measles immunization and population size, from the District Health Information System. A Bayesian hierarchical Poisson model was used to investigate the association between the risk of measles in infants in a district and first-dose vaccination coverage, population density, background prevalence of human immunodeficiency virus (HIV) infection and expected failure of seroconversion. Model projections were used to identify emerging high-risk areas in 2012.

FINDINGS: A clear spatial pattern of high-risk areas was noted, with many interconnected (i.e. neighbouring) areas. An increased risk of measles outbreak was significantly associated with both the preceding build-up of a susceptible population and population density. The risk was also elevated when more than 20% of infants in a populous area had missed a first vaccine dose. The model was able to identify areas at high risk of experiencing a measles outbreak in 2012 and where additional preventive measures could be undertaken.

CONCLUSION: The South African measles outbreak was associated with the build-up of a susceptible population (owing to poor vaccine coverage), high prevalence of HIV infection and high population density. The predictive model developed could be applied to other settings susceptible to sporadic outbreaks of measles and other vaccine-preventable diseases.