兒童嚴重急性呼吸道症候群臨床研究

Abstract

目的：嚴重急性呼吸道症候群(Severe acute respiratory syndrome, SARS) 是一新興感染症，其致病原為新發現的冠狀病毒(SARS-associated coronavirus)。許多呼吸道病毒的主要宿主均為兒童， 然而目前嚴重急 性呼吸道症候群的通報病例及研究成果多在成人，對其在兒童與青少年的 臨床表徵了解不多。因發燒是兒童相當常見的症狀，其中肺炎又是兒童常見之疾 病，因為兒童SARS 的診斷不易且常易與其餘非典型肺炎如黴漿菌或病毒性肺炎 相混淆，為了能使兒童SARS 之診斷能更加快速及準確，故本計畫將發展成本較 低、操作簡便、敏感性及特異性高的抗體偵測方法 – 即IFA (間接免疫螢光測 試)及ELISA (酵素免疫測試)，以作為SARS 流行期間快速診斷的依據。在有方 便可靠的抗體偵測工具後，本計畫將針對兒童SARS 研究其清流行病學及臨床特 徵，並追蹤其傳染途徑及傳染力。 方法：本研究IgG 抗體測試採用間接免疫螢光法(IFA)，為偵測此法敏感性 及特異性，採17 位內科SARS 病患恢復期血清作為陽性對照，204 位兩年前收 集之18 歲以下兒童血清作為陰性對照，測試結果敏感性及特異性均為100%。本 計畫自2003 年4 月開始一年內，針對十八歲以下的病患於研究期間於小兒科住 院或至急診就診者，收集其血清進行IgG 測試，以了解SARS 血清流行病學，對 於IgG 陽性者分析其臨床特性並收集家族成員血清進行研究，以釐清傳染途徑。 同時發展操作簡便的酵素免疫法(ELISA)，測試其最佳的反應條件以達最好的敏 感性及特異性。 結果：經調整緩衝液成分及反應時間後，使用全病毒抗原之ELISA 可達 96.4%的敏感性及100%的特異性。在偵測兒童SARS 病例方面，自2003 年4 月 至10 月，共收集422 位病患血清，179 位為呼吸道感染，137 位為非呼吸道感染 症，101 位為非感染症，共有七位IgG 陽性或培養及PCR 陽性，佔所有病患 1.66%，呼吸道病患2.79%。所有病患臨床症狀與一般肺炎難以區別，無一需要 插管呼吸器，且所有皆完全復原。合併感染比率在小兒科病患相當高(4/5)，推測 可能無合併感染症狀皆較輕微而不需至大醫院就診。所有病童家族成員血清皆為 陰性反應，表示沒有家族成員間的傳播。另外所有血清陽性且診斷肺炎者皆在 2003 年7 月之前，表示7 月之後即無新增SARS 病例。 結論：在2003 年SARS 流行期間小兒感染比例低。其症狀不具特異性，雨 一般肺炎難以區別。小兒科SARS 病症較成人輕微且較不具傳染性，合併感染比 例高，並未發現有家族內傳播的情形。使用ELISA 測定SARS-CoV 抗體是一操 作簡便同時具有高敏感性及特異性的檢查，在SARS 流行期間可作為快速診斷的 參考，也可作為調查SARS 流行病學的工具。

Background and purpose: Severe acute respiratory syndrome (SARS) is an emerging infectious disease caused by a novel SARS-associated coronavirus (SARS-CoV). In contrast to most viral diseases, clinical data about SARS are limited to adults and little about pediatric SARS have been reported. The purpose of this study is to identify the seroepidemiology and clinical features of SARS in pediatric patients. We also tried to clarify the transmission route and infectivity of pediatric SARS patients. Meanwhile, fever and pneumonia are common diseases in children. It is challenging to distinguish SARS from other respiratory tract infections in pediatric populations during the outbreak period. Therefore, we also try to develop the reliable and easy to perform tools for rapid diagnosis of SARS and epidemiological study. Methods: We collected blood samples from patients younger than 18 years old and admitted to National Taiwan University Hospital pediatric wards or visited pediatric emergency department. Serum IgG to SARS-CoV was tested by indirect immunofluorescent assay (IFA). The sensitivity and specificity of IFA were detected by the 86 sera from documented adult SARS patients and the 204 negative sera collected 2 years ago. Both the sensitivity and the specificity were 100%. Virus culture or detection of viral RNA by PCR from throat or nasopharyngeal swabs was done in some patients. We analyzed the clinical features of the cases with positive antibody response or culture/PCR result and measured the antibodies of family members living in the same household with the index case. We also test the different reagents and reaction intervals to optimize the performance of the IgG ELISA. Results: After adjusted the buffer contents and the reaction intervals, the IgG ELISA reached the sensitivity of 96.4% and the specificity of 100%. From April 2003 to October 2003, a total of 422 serum samples were collected. Six patients were seropositive for IgG anti-SARS CoV and one excreted SARS CoV in the feces. Among them, 5 patients were experiencing pneumonia. They accounted for 1.66% of all patients and 2.79% of the patients with respiratory tract infections. The clinical features of SARS patients were not specific. None of the SARS patients developed respiratory failure. However, coinfections with other pathogens were common in pediatric SARS patients (4/5). All the family members of the index case had negative antibody response. Conclusion: Few children were infected during the outbreak period in Taiwan in 2003. Pediatric SARS patients usually ran a benign disease course. The clinical features were not specific to distinguish SARS from pneumonia caused by other pathogens. Coinfection was common. Pediatric SARS patients were less contagious than adult patients. No intra-familial spread was documented. The whole virus antigen IgG ELISA is easy to perform and with high sensitivity and specificity. It can be used for rapid diagnosis during the SARS outbreak period and for seroepidemiology study.