Sharing experiences: towards an evidence based model of dengue surveillance and outbreak response in Latin America and Asia

Abstract

Background: The increasing frequency and intensity of dengue outbreaks in endemic and non-endemic countries requires a rational, evidence based response. To this end, we aimed to collate the experiences of a number of affected countries, identify strengths and limitations in dengue surveillance, outbreak preparedness, detection and response and contribute towards the development of a model contingency plan adaptable to country needs.

Methods: The study was undertaken in five Latin American (Brazil, Colombia, Dominican Republic, Mexico, Peru) and five in Asian countries (Indonesia, Malaysia, Maldives, Sri Lanka, Vietnam). A mixed-methods approach was used which included document analysis, key informant interviews, focus-group discussions, secondary data analysis and consensus building by an international dengue expert meeting organised by the World Health Organization, Special Program for Research and Training in Tropical Diseases (WHO-TDR).

Results: Country information on dengue is based on compulsory notification and reporting ("passive surveillance"), with laboratory confirmation (in all participating Latin American countries and some Asian countries) or by using a clinical syndromic definition. Seven countries additionally had sentinel sites with active dengue reporting, some also had virological surveillance. Six had agreed a formal definition of a dengue outbreak separate to seasonal variation in case numbers. Countries collected data on a range of warning signs that may identify outbreaks early, but none had developed a systematic approach to identifying and responding to the early stages of an outbreak. Outbreak response plans varied in quality, particularly regarding the early response. The surge capacity of hospitals with recent dengue outbreaks varied; those that could mobilise additional staff, beds, laboratory support and resources coped best in comparison to those improvising a coping strategy during the outbreak. Hospital outbreak management plans were present in 9/22 participating hospitals in Latin-America and 8/20 participating hospitals in Asia.

Conclusions: Considerable variation between countries was observed with regard to surveillance, outbreak detection, and response. Through discussion at the expert meeting, suggestions were made for the development of a more standardised approach in the form of a model contingency plan, with agreed outbreak definitions and country-specific risk assessment schemes to initiate early response activities according to the outbreak phase. This would also allow greater cross-country sharing of ideas.

Figure 1

Illustration of the seasonal variation of a vector borne disease like dengue. An example of an ‘endemic channel’ is shown here. The ’expected increase in cases’ usually coincides with, or follows, the rainy season. The shaded area corresponds to an ‘alarm zone’ where case numbers reach levels above the mean (or median) of a preceding time period (for example 5 years). The ‘epidemic zone’ is entered when case numbers reach levels above 2 standard deviations (or the third quartile).

Figure 2

An example of an outbreak curve of case numbers from the Dominican Republic is shown here. The number of new cases crosses the “historical” +2SD line from week 1 to 17 several times before, in week 18, the case numbers definitively rise.

Figure 3

Illustration of the different phases of a dengue outbreak and different levels of response. An example of an outbreak curve from Colombia in 2009 is shown here. An ‘outbreak alert’ is identified early through a combination of ‘alert signals’, and triggers an ‘initial response’. The evolution into ‘early’ and ‘full outbreaks’ are detected early using standard definitions and trigger appropriately staged ‘early’ and ‘emergency responses’.

Figure 4

Essential elements of a surveillance and preparedness system to ensure an early, staged outbreak response.