Establishing an early warning alert and response network following the Solomon Islands tsunami in 2013.

PROBLEM: On 6 February 2013, an 8.0 magnitude earthquake generated a tsunami that struck the Santa Cruz Islands, Solomon Islands, killing 10 people and displacing over 4700. APPROACH: A post-disaster assessment of the risk of epidemic disease transmission recommended the implementation of an early warning alert and response network (EWARN) to rapidly detect, assess and respond to potential outbreaks in the aftermath of the tsunami. LOCAL
SETTING: Almost 40% of the Santa Cruz Islands' population were displaced by the disaster, and living in cramped temporary camps with poor or absent sanitation facilities and insufficient access to clean water. There was no early warning disease surveillance system. RELEVANT CHANGES: By 25 February, an EWARN was operational in five health facilities that served 90% of the displaced population. Eight priority diseases or syndromes were reported weekly; unexpected health events were reported immediately. Between 25 February and 19 May, 1177 target diseases or syndrome cases were reported. Seven alerts were investigated. No sustained transmission or epidemics were identified. Reporting compliance was 85%. The EWARN was then transitioned to the routine four-syndrome early warning disease surveillance system. LESSON LEARNT: It was necessary to conduct a detailed assessment to evaluate the risk and potential impact of serious infectious disease outbreaks, to assess whether and how enhanced early warning disease surveillance should be implemented. Local capacities and available resources should be considered in planning EWARN implementation. An EWARN can be an opportunity to establish or strengthen early warning disease surveillance capabilities.

Introduction

On 6 February 2013, an 8.0 magnitude earthquake generated a three-metre tsunami that struck the remote Santa Cruz Islands (population 11 578, 2009 census) in the south-eastern Solomon Islands. The tsunami destroyed or damaged 1168 homes, severely damaged or destroyed water sources, and disrupted sanitation facilities. Ten people were killed and over 4700 were displaced.

Despite debate over the magnitude of epidemic risk in the post-disaster setting,– increased communicable disease transmission has been well documented. Thus, it is recommended that a detailed assessment to quantify epidemic risk be quickly conducted, after acute life-saving and initial rapid-assessment activities. If indicated, based on the findings of the risk assessment, a post-disaster early warning alert and response network (EWARN) should be implemented to rapidly identify and control disease epidemics.

Given the potential for enhanced disease transmission, the Solomon Islands Ministry of Health and Medical Services requested assistance from the World Health Organization (WHO) to assess and, as necessary, mitigate post-disaster epidemic risk. On 19 and 20 February 2013, a joint, on-site Ministry of Health and Medical Services and WHO assessment identified multiple post-disaster conditions that increased the risk of an epidemic, and recommended implementation of a post-disaster EWARN. We describe here the implementation, monitoring and results of the Santa Cruz Islands post-disaster EWARN, and key lessons learnt.

Approach

Epidemic risk assessment

The post-disaster risk assessment identified several factors that increased the risk of epidemic disease transmission. These included limited access to clean water, poor sanitation, high population density in displaced camps, living in bush, scrub and muddy environments, and increased exposure to disease vectors. The increased risk of an epidemic and the absence of early warning disease surveillance were the key findings when considering EWARN implementation.

Development of strategy

Senior provincial medical and public health staff worked closely with a WHO epidemiologist to develop an EWARN strategy and implementation plan. The objective was to establish a simple and streamlined surveillance network to assure timely identification of and response to potentially serious disease epidemics. A chaotic post-disaster setting and substantially reduced resources precluded comprehensive disease monitoring. Given the local context and limitations, simplicity was considered essential for successful implementation and operation of the EWARN.

Reporting sites

Criteria for EWARN site selection included proximity to displaced people and catchment population, and communication capabilities, including mobile phone network, long-wave radio or road connection to the EWARN coordination centre based at the provincial hospital. Five health facilities were selected: the provincial hospital, three health centres and one nursing station, all of which had reliable communication capabilities. The estimated EWARN catchment population was 8000 people, and it included 90% of the 4700 who had been displaced.

Selection of diseases

Eight target diseases and syndromes were selected based on severity (life-threatening or potentially life-threatening), transmission potential (epidemic or possible epidemic capacity) and relevance to the post-disaster setting (present or likely present), as described in the post-disaster risk assessment. Target diseases included malaria, suspected dengue and suspected scrub typhus; target syndromes included influenza-like illness, watery diarrhoea, bloody diarrhoea, acute fever and rash, and prolonged fever. A case definition was established for all target diseases and syndromes (for more information contact author). In addition, event-based surveillance collected ad hoc information on health events or potential risks to health, including unexpected deaths, clusters of unusual or severe disease, chemical spills, and bird, fish or animal die-offs.

Defining alerts

An alert was defined as “an increase in number of cases of a specific disease or syndrome beyond what was expected for that reporting site, based on trends in weekly target diseases and standardized thresholds.” Site-specific thresholds based on historical data could not be calculated because of the absence of pre-disaster surveillance data. Any unexpected event reported through the event-based surveillance was treated as an alert.

Implementation

Between 21 and 24 February 2013, a joint Ministry of Health and Medical Services and WHO team implemented the EWARN. A senior public health nurse was identified as the EWARN coordinator, responsible for data collection, alert verification, monitoring and response coordination. Two-hour trainings for all Ministry of Health and Medical Services staff involved in the EWARN were conducted at each of the five EWARN sites to review the target diseases and syndromes, case definitions, criteria for unexpected events, data collection forms, reporting procedures and timelines. A local outbreak response team – comprising nursing, health promotion, logistics, and environmental health staff – was established. Also, a half-day training was conducted on EWARN alert verification, and on how to perform investigations and implement rapid control measures. Challenges to EWARN implementation were largely transportation-related; that is, they were related to difficulties in accessing the rural health facilities due to a shortage of available vehicles, competing priorities in the post-disaster phase or a lack of the fuel for the outboard motors needed to visit the northern and eastern villages and health facilities that are remote and accessible only by sea. These challenges were resolved by the provincial nursing director, the most senior Ministry of Health and Medical Services staff on the Santa Cruz Islands, who had the authority to identify and release the necessary resources.

Data procedure

Cases that met the case definition for a target disease or syndrome were stratified by age (less than 5 years, 5–14 years and more than 14 years of age), and recorded on a tally sheet and line list. Surveillance data were communicated weekly via the EWARN coordinator to the Ministry of Health and Medical Services National Surveillance Unit in the capital Honiara, which analysed data and monitored for (and assured verification of) any alert. Any unusual or unexpected event was immediately reported to the EWARN coordinator.

Surveillance outputs

Between 25 February and 19 May 2013 (after 12 weeks of EWARN operations), a total of 1177 target diseases or syndrome cases were registered from a total of 5323 estimated consultations. Influenza-like illness was most commonly reported (626 cases, 11.8% of consultations) followed by watery diarrhoea (171 cases, 3.2%), malaria (94 cases, 1.8%), acute fever and rash (90 cases, 1.7%), prolonged fever (90 cases, 1.7%), suspected dengue (57 cases, 1.1%), suspected scrub typhus (32 cases, 0.6%) and bloody diarrhoea (17 cases, 0.3%); the remainder of the consultations (4146, 77.9%) were for other causes.

Seven alerts were generated, verified and, as necessary, investigated: watery diarrhoea (2 alerts), bloody diarrhoea (1 alert), acute fever and rash (1 alert), prolonged fever (1 alert), suspected dengue (1 alert) and influenza-like illness (1 alert). No unusual or expected events were reported through the event-based surveillance. Alerts were verified by asking the relevant health-care providers to confirm the data and provide additional information on clinical features, disease severity, and whether the number of new cases was increasing or decreasing. Verified alerts with evidence of ongoing transmission were investigated by the EWARN outbreak response team. The dengue-like illness alert was a reporting error. Of the six verified alerts, four events were isolated and the rate of new cases returned to baseline without intervention. The two remaining alerts required the investigation team to be dispatched and control measures implemented. None of the alerts progressed to sustained transmission; therefore, no laboratory samples were collected by the investigation teams. Fifty-one weekly reports were received (51/60, 85% reporting compliance) within 24 hours of the weekly reporting deadline. The remaining nine reports (15%) were not received.

Discussion

We implemented an EWARN that included indicator and event-based surveillance components two weeks after an earthquake and tsunami, despite limited human, medical, laboratory and logistical capacities; a remote setting; and a challenging post-disaster context. Several alerts were reported and investigated, but none led to sustained transmission. In May 2013, a repeated risk assessment found a decreased risk of epidemic transmission. On 20 May, the EWARN was transitioned to a four-syndrome early warning disease surveillance system that aligns with the Solomon Islands and Pacific Syndromic Surveillance Systems. These systems monitor influenza-like illness, diarrhoea, acute fever and rash, and prolonged fever plus any unexpected or unusual event with potential health implications.

One limitation of the EWARN was an absence of baseline surveillance data to establish alert thresholds (weekly trends and existing standard reference materials were used instead). Another limitation was that site-selection criteria may have introduced an unintended bias that systematically recruited sites at higher or lower risk of outbreaks. For example, sites and communities with reliable communication may have better water and sanitation infrastructure that would in turn systematically decrease the risk of enteric disease outbreak in those communities. Also, the EWARN did not capture all affected populations, and localized outbreaks may have been missed.

Certain post-disaster features (e.g. population displacement, crowded living conditions, limited clean water and poor sanitation) increase the risk of an epidemic.– Hence, an assessment is necessary to quantify the risk and, as appropriate, guide mitigation interventions. Important factors when considering EWARN implementation include magnitude of epidemic risk, existing capacity to identify and respond, and available resources. Post-disaster environments are usually resource-scarce; thus, any activity should consider resource implications. Immediate post-disaster environments are typically dynamic, with ongoing population movement and changes in epidemic risk characteristics (including water quality and quantity, hygiene, sanitation and access to health care). Therefore, the timing of a risk assessment has implications for estimation of the risk of an epidemic and consideration of risk mitigation.

Given the substantial human, material and financial resources mobilized in a disaster response, it is important to link post-disaster activities to long-term development goals. EWARN systems, as one element of a disaster response, are well suited to building or strengthening sustainable early warning disease surveillance and response, and thereby help countries meet their International Health Regulation obligations to achieve and maintain essential surveillance and response capacity. As with all surveillance systems, ongoing monitoring, assessment, feedback and training is necessary to assure sustainability.

We learnt several lessons that will be useful when considering post-disaster early warning disease surveillance (Box 1). First, promptly conducting a detailed assessment to evaluate the risk and potential impact of serious infectious disease outbreaks is necessary to assess whether and how enhanced early warning disease surveillance should be implemented. Second, local capacities and available resources should be considered in planning EWARN implementation. Finally, an EWARN can be an opportunity to establish or strengthen sustainable early warning disease surveillance capabilities. No pre-earthquake disease surveillance was operational on the Santa Cruz Islands. However, the EWARN established a surveillance infrastructure and, after three months of operation, it was smoothly transitioned, with minimal additional financial or material resources, into the routine Solomon Islands Syndromic Surveillance System.

A detailed assessment to evaluate the risk and potential impact of serious infectious disease outbreaks is necessary to assess whether and how enhanced early warning disease surveillance should be implemented.

Local capacities and available resources should be considered in planning EWARN implementation.

An EWARN can be an opportunity to establish or strengthen early warning disease surveillance capabilities.

EWARN, early warning alert and response network.