2001-2005年北京地区婴幼儿甲型流感病毒感染的研究

目的 通过连续的监测,了解北京地区婴幼儿甲型流感的流行规律。方法 2001年10月—2005年8月,采集门诊和住院急性呼吸道感染患儿的标本7338份,分别经传代狗肾细胞进行病毒分离和（或）间接免疫荧光、血凝抑制试验进行流感病毒型别鉴定,采用RT-PCR方法,扩增甲3型流感病毒流行株的血凝素基因HA1区,进行序列分析。结果 （1）从7338份临床标本中,检出甲型流感病毒347份,总阳性率为4．7％。347份甲型流感病毒中,甲1型48份（13．8％）;甲3型273份（78．7％）;暂时无法鉴定亚型的26份（7．5％）。（2）2001-2004年的流行比较局限在当年10月至次年4月,2004年8月—2005年8月均有甲型流感病毒被检测到,在夏季仍可检测到相当多的甲型病毒,尤其是2005年8月甲3型的阳性率达到14．2％,相当于2003-2004年的流行最高峰。4年中每个流行季节都以甲3型流感病毒的流行为主,只在2001-2002年和2004-2005年的流行季节出现了甲1型流感病毒的流行峰。（3）甲1和甲3型流感病毒在门诊患儿中的阳性检出率均高于住院患儿的阳性检出率。在2003年11月—2005年8月期间的236例甲3型感染患儿中,≤2岁者占46．6％,〉5岁者占14．0％;而31例甲1型感染患儿中≤2岁者只占6．5％,〉5岁者占48．0％。（4）对1998-2005年的甲3型流感病毒血凝素基因HA1区的序列分析显示,每一年的甲3型病毒都会出现位于其抗原决定簇关键位点的氨基酸突变。结论2001年10月—2005年8月,北京地区婴幼儿中有甲1和甲3型流感不同程度的流行,甲3型为优势流行株;2004-2005年北京地区甲型流感呈全年的流行态势;氨基酸序列分析提示,1998-2005年期间甲3型流感病毒的抗原性在持续不断地发生漂移。

Surveillance for influenza A virus infections in infants and young children in Beijing, China, 2001-2005

Objective To characterize the prevalence and antigenic drift of influenza A viruses isolated during the period from 2001 to 2005 in infants and young children in Beijing. Methods MDCK cell culture, indirect immunofluorescence assay (IFA) and hemagglutination inhibition (HI) assay were used to isolate and identify type A influenza viruses ( H1N1 and H3N2) from clinical samples collected from outpatients and inpatients who visited the Affiliated Children' s Hospital because of acute respiratory infections from Oct 2001 to Aug. 2005. The HA1 regions of hemagglutinin gene of H3N2 isolates were amplified by using RT-PCR followed by sequencing. Results Out of 7338 clinical samples collected during this surveillance period, 347 (4.7%) were positive for influenza A viruses, including 48 (13.8%) of H1N1, 273 (78. 7% ) of H3N2 and 26 (7. 5% ) of subtype-unidentified influenza A viruses. Although there was a prevalence season of influenza A from October each year to April of next year during the 2001-2004 period, it was worth noting that a consecutive influenza A activity was detected from Aug. 2004 to Aug. 2005, when some influenza A viruses were detected even in summer. The positive rate of H3N2 was 14. 2% in August, 2005, which was equal to that of the peak season of 2003-2004. H3N2 were predominant in most of the influenza seasons during the surveillance period, and H1N1 was detected only in the influenza seasons of the 2001-2002 and 2004-2005 along with H3N2. The positive rates for both H3N2 and H1N1 were higher in specimens from outpatients than those from inpatients. A total of 46. 6% ( 110/236) of the H3N2 were detected from children younger than 2 years of age, and 14. 0% (33/236) were from children older than 5 years, whereas,more H1N1 was found in children older than 5 years (48. 0% ,12/31) than in those younger than 2 years (6. 5% ,2/31) during a period from Nov. 2003 to Aug. 2005. Sequence analysis of the HA1 regions of hemagglutinin of H3N2 isolated in a series of years revealed amino acid changes in the HA1 domain of H3N2 isolates in the antigenic sites (A-E) each year. Conclusion H3N2 and H1N1 prevailed in each influenza season during the surveillance period in Beijing, and H3N2 strains were predominant The data from all-year around surveillance of influenza in Beijing indicate that continuous surveillance throughout a year and use of both antigenic and molecular analysis will be more helpful for early identification of any antigenic variants as well as prevention and control of influenza by promoting development of vaccines.