Tuberculin skin test in close contacts in case of school tuberculosis outbreak

Abstract

Objective To evaluate the role of tuberculin skin test prified-protein derivative (PPD) in defining the screening scope of close contacts of tuberculosis cases in disposal of tuberculosis outbreak in schools.

Methods In a senior middle school in August 2019, 1 553 students of the grade two were tested by PPD because of a school tuberculosis outbreak. PPD results were compared to grade one students without any association with this tuberculosis epidemic, who were also tested by PPD when beginning school. Potential association between PPD distribution characteristics and tuberculosis case distribution were analyzed.

Results Twenty-nine grade two students were diagnozed as tuberculosis infection, seven of which were PPD-positive, and with the same MIRU-VNTR genotype. In grade one, 0.1% (1/796) student showed strong PPD-positive, 34.3% (273/796) student showed positive. For grade two students, significant higher rate of strong PPD-positive [5.9% (45/757)], and PPD-positive [52.0% (394/757) ] were observed (χ ²=45.71, 49.90, P<0.01). Proportion of strong PPD-positive in the first floor of the teaching building (19.4%), where tuberculosis cases clustered, was significantly higher than that in other floors (χ ²= 89.81, P<0.01); Number of strong PPD-positive students increased with TB cases in each floor of the teaching building ( r = 0.99, P<0.01). Proportion of strong PPD-positive and PPD-positive in floors of the dormitory, where TB cases lived, was significantly higher than in other floors (χ ² = 49.4, 64.9, P<0.01). Number of strong PPD-positive and PPD-positive students increased with TB cases in each floor of the teaching building ( r = 0.84, 0.56, P<0.01).

Conclusion Strong PPD-positive rate well reflects tuberculosis infection of close contacts, and is recommended for defining the scope of screening.

Abstract

【摘要】 目的 探索结核菌素试验 (PPD 试验) 在学校结核病疫情处置中对于界定密切接触者筛查范围的作用, 为学校肺 结核防治工作提供参考依据。 方法 回顾性分析比较 2019 年 8 月广东省某中学发生肺结核疫情的高二年级与同期该校 高一入学新生体检 PPD 试验结果, 共 1 553 名学生, 并评估高二年级学生 PPD 试验流行病学分布与肺结核病例分布之间 的潜在关联。 结果 高二年级结核病疫情共确诊学生患者 29 例, 其中 7 例病原学阳性, 且菌株 MIRU-VNTR 基因分型相 同。高一年级学生人群中 PPD 强阳性率为 0.1%, PPD 阳性率为 34.3%; 高二年级学生人群 PPD 强阳性率、阳性率分别为 5.9%, 52.0%, 高二年级均高于高一年级, 差异均有统计学意义 (χ ² 值分别为 45.71, 49.90, P 值均<0.01)。在教学楼分布方 面, 疫情发源、病例集中的教学楼一层学生 PPD 强阳性率为 19.4%, 远高于教学楼其他楼层, PPD 强阳性率逐楼层持续降 低, 差异有统计学意义 (χ ² = 89.81, P<0.01); 各楼层的 PPD 强阳人数与学生病例数量呈正相关 ( r = 0.99, P<0.01)。在宿舍 楼层分布方面, 病例所在的宿舍楼层学生人群 PPD 强阳性率、阳性率明显大于无病例的楼层, 差异有统计学意义 (χ ² 值分别为 49.4, 64.9, P 值均<0.01); 各宿舍楼层 PPD 强阳人数、阳性人数与各层肺结核病例数之间呈正相关 ( r 值分别为 0.84, 0.56, P 值均<0.05)。 结论 PPD 强阳性率可以良好地反映学校肺结核密切接触人群结核杆菌感染和疫情扩散的情况, 建 议作为考量扩大密切接触者筛查范围的因素之一。