Temporal trends in dengue incidence and mortality across surveillance case classifications: a 13-year analysis from Davao City, Philippines

Abstract

Dengue remains a major public health concern in the Philippines, where routine surveillance systems classify reported cases as suspected, probable or confirmed. Although these classifications are widely used to monitor disease burden, their influence on the interpretation of long-term epidemiological trends and mortality patterns remains unclear. This study examined the temporal trends in dengue incidence and mortality across surveillance case classifications in Davao City, Philippines, over a 13-year period. A retrospective observational study was conducted using dengue surveillance data collected from the Philippine Integrated Disease Surveillance and Response (PIDSR) system from January 2012 to December 2024. Reported dengue cases were classified as suspected, probable, or confirmed, according to the national surveillance definitions. Annual dengue incidence and mortality were calculated per 100,000 population, and temporal trends were assessed using the Mann–Kendall trend test. A total of 81,075 dengue cases were reported during the study period, including 59,021 suspected, 20,559 probable, and 1,495 confirmed cases. Confirmed dengue incidence exhibited a significant increasing trend over time ( p  = 0.003), whereas probable ( p  = 0.855) and suspected dengue incidences ( p = 0.059) showed no statistically significant temporal trends. Increasing trends in confirmed dengue incidence were consistently observed across congressional districts, age groups, and sexes. Dengue mortality incidence showed no significant temporal trends in suspected ( p  = 0.089), probable ( p  = 0.242), or confirmed cases ( p  = 0.282). Most deaths recorded among reported dengue notifications occurred among probable and suspected cases, and the highest cumulative case fatality rate was observed among probable cases (0.89%). Surveillance classifications captured distinct epidemiological patterns of dengue incidence and mortality. In low- and middle-income country (LMIC) settings, where surveillance systems operate under varying levels of diagnostic certainty, considering probable and suspected case classifications may provide additional insights into surveillance trends and mortality patterns beyond those obtained from laboratory-confirmed cases.