患者，男，40岁，上海市居民。2018年7月因“急性腹泻”就诊于同济大学附属杨浦医院急诊内科。患者自述水样便腹泻1 d。患者发病前1个月有巴拿马旅行史，无饮生水和食生肉史。血常规检查结果C反应蛋白升高（16.17 mg/L），其余指标正常，提示感染。患者粪样涂片镜检查见蓝氏贾第鞭毛虫包囊和滋养体。间接免疫荧光试验检测结果显示，蓝氏贾第鞭毛虫滋养体被患者血清（1∶50）识别，虫体表面有较强的荧光染色。提取患者粪样DNA，PCR扩增出147 bp的蓝氏贾第鞭毛虫特异性18S核糖体基因片段，该片段序列与蓝氏贾第鞭毛虫集聚体A（GenBank登录号：KY706490）的序列一致性为100%，在邻接法构建的系统进化树上与蓝氏贾第鞭毛虫集聚体A聚在同一分支上。结合患者临床表现和相关检查结果，诊断患者为蓝氏贾第鞭毛虫感染。临床给予患者甲硝唑（每日20 mg/kg，分3次口服，连服7 d）治疗。2周后复查血常规和粪便常规，均恢复正常，患者病情好转。

A 40-year-old male, who is a Shanghai resident, presented to the emergency department of Yangpu Hospital, School of Medicine, Tongji University in July 2018. The patient complained of watery diarrhea for 1 day. The patient had a travel history to Panama one month before the onset of the disease and had no history of drinking unboiled water or consuming uncooked meat. The routine blood cell count results were normal except for an increase in C-reactive protein of 16.17 mg/L (normal value 0-10 mg/L), which indicated an infection. Giardia trophozoites and cysts were found in stool specimens by microscopic examination. The IFA test results showed that G. lamblia trophozoites was recognized by the patient’s serum (1 ∶ 50), and there was strong fluorescence staining on the surface of G. lamblia. A 147 bp fragment of Giardia-specific 18S ribosomal RNA was amplified by PCR. The sequence of this fragment was 100% consistent with the sequence of G. lamblia assemblage A (GenBank login number: KY706490), and it was clustered on the same branch with G. lamblia assembly A in the phylogenetic tree constructed by the neighbour-joining method. Based on the patient’s clinical manifestations and relevant examination results, a G. lamblia infection diagnosis was made. The patient was treated with oral metronidazole at 20 mg/kg daily, divided into 3 doses and take for 7 days. Blood and fecal routine tests were re-examined two weeks later, and both results returned to normal. The patient’s condition was improved without recurrence of symptoms.