Objective To compare PPD conversion with γ-interferon release assay (IGRA) in determining the newly Mycobacterium tuberculosis (MTB) infection during a TB outbreak. Methods The 505 subjects exposed to a TB outbreak were divided into 3 groups based upon the induration diameters of PPD before the outbreak.The changes of PPD induration diameters were observed in different groups,and correlation between PPD conversion or IGRA and exposure levels were analyzed by logistic regression.Results In subjects with the highest exposure level,the increase in induration of PPD was ( 12 ±5) mm,(7±4) mm,and (5±3) mm respectively among the previous PPD ＜5 mm,5- ＜10 mm,and ≥10 mm groups,the difference being significant among groups,x2 =43.12,P ＜ 0.01. Using logistic regression analysis,PPD conversion was related to the exposure level ( OR =4.70,P ＜ 0.05 ) only in the PPD ＜ 5 mmgroup,while IGRA positivity was closely related to the exposure levels in all 3 groups (OR values were 2.16 -3.60,P ＜0.05 ).In the high exposure group,the subjects with IGRA positivity combined with PPD conversion rate was 26.1％ (31/119 ),and the subjects with IGRA positivity but no PPD conversion rate was 39.5％ (47/119),while in the low exposure group the results were 6.5％ (12/185) and 16.8％(31/185) respectively,the difference being significant ( x2 =22.82 and 19.63,P ＜0.01 ).After 1 year of follow-up,the reversion rate of the subjects with IGRA positivity was 48.1％ (91/189),while the mean increase value of PPD was ( 1.1 ± 4.0) mm. Conclusion IGRA is superior to PPD conversion in the diagnosis of tuberculosis infection,and more valuable in the detection of newly infected cases.%目的 比较PPD试验和γ-干扰素释放试验(IGRA)在结核病暴发事件中判断新近感染者的价值.方法 2010年4月大连市某大学分院发生结核病暴发事件,将505例接触者(年龄20～22岁)分为高暴露组119例,中暴露组201例,低暴露185例；再按照入学时(第1次)PPD试验硬结直径分为＜5 mm组143例,5～＜10 mm组205例,≥10 mm组157例.计算各组2次PPD结果的差值(净增值).组间比较采用Kruskal-Wallis秩和检验,率的比较采用x2检验,采用logistic回归方法进行相关性检验.结果 505例接触者暴发前PPD硬结直径平均值[(7 ±5) mm]显著低于暴发后[( 13±5)mm],差异有统计学意义(Z=- 18.13,P＜0.01).在结核病暴发前,高暴露组PPD试验硬结＜5 mm、5 ～＜10 mm和≥10 mm组的直径净增值分别为(12±5)mm、(7 ±4)mm和(5±3)mm,差异有统计学意义(x2=43.12,P ＜0.01).＜5 mm组的PPD试验阳转率与暴露等级有显著相关性(OR值为4.70,P＜0.05),而IGRA阳性与3个暴露组均有显著相关性(OR值为2.16～3.60,均P＜0.05).高暴露组中IGRA阳性同时伴PPD试验阳转率为26.1％(31/119),IGRA阳性伴PPD试验未阳转的检出率为39.5％ (47/119),而在低暴露组二者分别为6.5％ (12/185)和16.8％ (31/185),差异有统计学意义,(x2值分别为22.82、19.63,均P＜0.01).189例IGRA阳性者随访1年,阴转率为48.1％ (91/189),而PPD试验硬结直径净增值为(1.1±4.0)mm.结论 采用IGRA判断潜伏MTB感染优于PPD试验阳转,可以早期识别新近感染者.
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