研究背景
臺灣幾乎每年都有因境外移入的病例而間接造成大小不一的本土性登革熱流行，然而有症狀而且被通報的病人往往只是登革熱疫情的冰山一角，文獻回顧顯示登革病毒感染人體時約有50-75%屬於無症狀感染，故藉由社區血清流行病學才能真正了解登革熱造成的影響。回顧臺灣登革熱相關文獻後，發現臺灣登革熱血清流行病學的資料十分有限，其中又大多針對高屏兩地，台南市登革熱的資料較少。因此本研究於2015年台南巿登革熱流行期之末期執行血清流行病學調查，以了解本次登革熱流行的實際流行狀況及未通報登革熱感染者（含無症狀感染及有症狀但未通報）比例，以作為未來防治及下次流行預測的政策參考。
研究方法
本研究屬橫斷性調查，採用方便取樣，收案時間從2015年10月中至11月底，屬於2015年臺南市登革熱大流行末期。收案地點為臺南市中西區、北區、東區、永康區和安南區，最後實際分析人數為1520人。所有血液檢體使用酵素結合免疫吸附法（ELISA）檢測是否含有IgM和IgG抗體，以了解受試者是否最近或之前有感染登革熱。我們也使用即時反轉錄聚合酶鏈鎖反應檢驗（Real-time RT–PCR）檢驗是否含有登革熱病毒及病毒量的高低。
結果
IgM陽性率佔6.45%（98/1520）且隨年齡的增加有顯著上升的趨勢，顯示臺灣老年人近期有比較容易被感染的情形；IgG陽性率佔16.32%（248/1520）且同樣有隨年齡的增加有顯著上升的趨勢。收案的五個行政區之血清盛行率不同且在流行區與非流行區的流行程度差異頗大。我們估計2015年臺南市熱區(含中西區、北區和東區)的未通報率為2.37，換句話說，此次疫情若發現一個通報病例，背後就會有超過兩位的未通報感染者出現；比較歷年通報資料與實際感染率的差異，發現臺南市熱區(含中西區、北區和東區)的實際感染率比歷年通報資料總共高出4.98倍。
結論
本研究發現臺灣的老年人在2015年的大流行中有比較容易被感染的情形，且2015年可能因為有採用大量免費快篩使得漏報的比例大幅降低，雖然因本研究之限制無法深入探究其原因，但在未來的研究及政策上亦可針對此現象深入探討或當作往後預防政策之參考。

The aim of this study was to investigate the seroepidemiology of dengue virus (DENV) infection in Tainan and to further analyze the ratio of unreported to reported dengue infection to estimate the true disease burden. A cross-sectional survey was conducted with convenience sampling. A total of 1520 serum specimens were collected from residents in five districts in Tainan city, including West Central, North, East, Yong-Kang and Annan districts from mid-October to November, 2015. Enzyme-linked immunosorbent assays were used to identify IgM and IgG antibodies against DENV to determine whether the participants had recent or past dengue infection. Real-time reverse transcription–polymerase chain reactions were also used to identify DENV. The percentage of positive anti-DENV IgM was 6.45% (98/1520) and the percentage increased markedly with age. The seroprevalence of anti-DENV IgG was 16.32% (248/1520) and increased markedly with age as well. The estimated ratios of unreported to reported dengue infection were 2.37 in the 2015 dengue epidemic and 4.98 in cumulative past dengue epidemics. Our study showed that elderly people in Tainan were more likely to be infected in 2015. It also suggested that unreported dengue infection decreased markedly probably due to widespread use of rapid tests in this epidemic.

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