Observations on surveillance systems
The core functions of a comprehensive surveillance system are detection, reporting, investigation, confirmation, analysis, interpretation, and response. Cooperation is essential between the healthcare system and the public health authority because for rapid response to emerging public health threats the public health authority is dependent on healthcare system to generate timely and accurate case reports.
Observations on diagnosis and case definitions of dengue
At the time of the meeting, WHO had published guidelines on the diagnosis of dengue including case definitions; but these guidelines were published more than 10 years ago 
—in 2009 WHO published new guidelines with major changes in dengue case classifications 
. Regional offices have also drafted guidelines 
. The guidelines agree on major issues with minor variations (for example, some include leukopenia or hepatomegaly in the case definitions, but not all include a “suspected case” category).
One major difficulty with all previous guidelines is case classification 
. Because case fatality rates are much higher among patients with DHF, correct classification is important for triage, treatment, and prognosis. Obtaining a platelet count, hematocrit, and radiographic imaging is often not possible, too time consuming, or too expensive in many healthcare facilities in endemic countries—but the results of these tests are required diagnostic criteria for DHF. There was wide recognition of the need for a simplified classification system that is still helpful for case management 
Although meeting attendees reported using similar dengue case definition systems, surveillance methods varied between countries. Laboratory methods also vary as well as the testing algorithms and the interpretation of positives. For example, in Brazil and Colombia, healthcare providers complete case reports on both ambulatory and hospitalized patients, however, in Thailand and Vietnam the majority of reported cases are hospitalized. In only 12/22 (55%) of countries represented at the meeting confirmed all officially reported cases with laboratory testing. Nearly every country includes suspected dengue cases regardless of age, but in Cambodia surveillance is conducted only among children less than 15 years of age. In Singapore and Brazil, monitoring vector indices is an integral part of the dengue surveillance system, while in Puerto Rico it is not. The attendees reported that these differences were not currently a problem for country level analyses but make inter-country, regional, and global analyses and comparisons difficult. Moreover, some difference (e.g. lack of dengue surveillance among adults in Cambodia) could be an impediment to strategic planning and implementation of a dengue vaccine since the disease also affects adults as well as children. Moreover, the vaccination of children is likely to also have an impact on adult disease burden 
, further improving the cost-effectiveness.
Since surveillance data are needed for health ministries to target control responses when outbreaks are detected, data must be collected in a timely fashion. In order to better understand the overall process, attendees reviewed the steps from infection to reporting (). The incubation period is, on average, one week following the bite of an infectious mosquito. Several more days pass before symptoms become severe enough to cause the patient to seek medical attention, and still more time is required for the symptoms of DHF to develop. Outpatient clinic-based surveillance will detect cases earlier than inpatient facilities, potentially allowing more time for public health action.
Timeline showing transmission cycle, clinical disease, and surveillance events.
The medium for reporting ranged from paper case report forms, to hand-held computers, to internet-based systems. A case study from Nicaragua showed that hand-held computers, although initially requiring significant investment in infrastructure and training, do reduce reporting time. In Kolkata, India, special mapping of cases has been used to target control activities. In Singapore and Brazil, ministries are also using intranet-based data entry software allowing staff to directly enter data on cases and Ae. aegypti breeding sites in the field. The data are then immediately available to plan interventions and follow-up. All countries are dependent on paper forms for case reporting before any additional investigation or action. Time is required for that report to reach the surveillance office, to be entered and analyzed, and finally be reported. However, many countries are developing improved methods for data collection for targeted interventions.
Another key issue is the needs of stakeholders with interests in dengue diagnosis and surveillance. These stakeholders include the general public, senior policy-makers, academics, and legislators. A diverse group, their interests range from the parents of sick children who want immediate and accurate test results—knowing the diagnosis allows them to cope better—to healthcare workers, staff in laboratories, public health and vector control authorities. All want a point-of-care test to speed accurate diagnosis and treatment and allow rapid public health intervention. Others (e.g. general public, including travellers and Ministries of Health) are more likely interested in more accurate tests to allow improved burden of disease estimates which could effect budget allocations for control.
In most countries diagnostic testing and surveillance relies on healthcare practitioners and laboratory staff to report cases but they receive little benefit. Confirmatory diagnostic tests such as virus isolation or reverse transcriptase-polymerase chain reaction testing (RT-PCR) require expertise and equipment usually found only in reference laboratories. However, several attendees explained that the time required for a sample to reach and to be processed at centralized facilities often results in delays that render the results useless to the treating physician. Further delays occur if the information provide on a sample is incomplete or if batch-testing of samples is conducted. After testing, the report generated requires verification, approval and delivery (e.g. mailing). As a consequence, health care providers in most countries must treat patients empirically 
The attendees concluded that simplified case reporting 
, rapid turnaround of results, and training healthcare providers in reporting 
can be important ways to encourage continued reporting of cases. Mandatory reporting, they explained, rarely guaranteed reporting.
Strengths and weaknesses of existing surveillance systems
Attendees were asked to identify the strengths and weaknesses of their systems. Most indicated that their countries had adequate infrastructure and surveillance systems, and the adjectives “dedicated”, “committed”, “skilled”, and “motivated” were widely used to describe the quality of the personnel engaged in surveillance. They reported some country-specific but effective links between the various stakeholders; especially healthcare providers, laboratory staff, and the public health and vector control authorities. However, many of these relationships are dependent on personal contacts which are affected by staff turnover.
A common perception among meeting attendees was that disease control is politically more important than prevention. That is, highly visible outbreak response through spraying is considered more important than outbreak prevention. Specifically, during outbreaks, public demand for action often leads to pesticide spraying 
which is unlikely to be effective since the pesticide released in the streets is unlikely to reach the adult mosquitoes resting and feeding inside homes 
Lack of preventive services in the provinces is seen as a further impediment to conducting adequate surveillance. Further, even when adequate infrastructure exists, data are rarely used locally; rather they are forwarded to the central ministry offices for official evaluation, missing the opportunity for an immediate local response. Diagnostic tests further complicate the situation because the results are often difficult to interpret by the healthcare providers and public health practitioners unfamiliar with the limitations of the tests 
. Lack of funding for laboratory confirmation of cases and having those services available only at central level were reported as further weaknesses. One participant remarked that local pubic health agencies in large countries such as Brazil have their response time greatly delayed if they must wait for laboratory confirmation at the national level. Indeed, while experts agreed that staff conducting surveillance were committed, under-detection and under-reporting of dengue cases were significant and often due to the design of the surveillance system and lack of funding. Also, data sharing and full coordination of entomologic surveillance conducted by vector control units and human disease surveillance conducted by epidemiologists is needed to improve detection of increased transmission sufficiently early to prevent or control outbreaks. Finally, virological surveillance is under-utilized or in some countries, completely lacking: It's importance emphasized by the fact that large outbreaks tend to follow changes or reintroductions of serotypes.