Van Wyk Hannah, Brouwer Andrew F, Lee Gwenyth O, Márquez Sully, Andrade Paulina, Ionides Edward L, Coloma Josefina, Eisenberg Joseph N S
From the Department of Epidemiology, University of Michigan School of Public Health Ann Arbor, MI.
Department of Biostatistics and Epidemiology, Rutgers Global Health Institute, Rutgers University, New Brunswick, NJ.
Epidemiology. 2025 Sep 1;36(5):636-645. doi: 10.1097/EDE.0000000000001874. Epub 2025 Jun 3.
Pathogen transmission of an outbreak generally begins well before it is identified by a surveillance system, particularly for infectious diseases in which a high proportion of cases are subclinical, as is the case for arboviruses. We aimed to ascertain the most likely date of the primary case (the first infection, whether detected or not) in an outbreak.
Using data from a 2019 dengue outbreak in a rural, riverine town in Northwestern Ecuador, we investigated potential undetected dengue virus transmission before the outbreak detected in mid-May. The outbreak was preceded by four reported cases on 9 February, 13 February, 28 March, and 2 May. Using a hidden Markov model, we estimate the most likely date of the primary case for different assumed case reporting fractions.
For all reporting fractions, the most likely primary case occurred near the 2 February candidate index cases, ranging from 7 February to 12 February, over 2 months before the main outbreak. Individual simulations showed that earlier and later primary cases were also possible. Our results suggest that the dengue virus was circulating in the community for around 3 months before the outbreak.
Surveillance systems that can detect low-level transmission in the early stages of an outbreak can provide time to intervene before the exponential phase of the outbreak, with the potential to substantially reduce transmission and disease burden.
疫情的病原体传播通常在监测系统识别之前就已开始，特别是对于许多病例为亚临床病例的传染病，虫媒病毒就是如此。我们旨在确定疫情中首例病例（首次感染，无论是否被检测到）最可能的日期。
利用厄瓜多尔西北部一个河边乡村小镇2019年登革热疫情的数据，我们调查了5月中旬疫情被检测到之前潜在的未被发现的登革热病毒传播情况。在此次疫情之前，分别于2月9日、2月13日、3月28日和5月2日报告了4例病例。我们使用隐马尔可夫模型，针对不同假定的病例报告比例，估计首例病例最可能的日期。
对于所有报告比例，首例病例最可能出现在2月2日候选指示病例附近，范围从2月7日至2月12日，在主要疫情爆发前两个多月。个体模拟显示，首例病例也有可能更早或更晚出现。我们的结果表明，登革热病毒在疫情爆发前已在社区传播约3个月。
能够在疫情早期阶段检测到低水平传播的监测系统，可以在疫情指数增长阶段之前提供干预时间，有可能大幅减少传播和疾病负担。
