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Chinese Journal of Antituberculosis ›› 2012, Vol. 34 ›› Issue (10): 637-641.

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Preliminary study on school tuberculosis group infection control strategy

LU Xi-wei, SONG Qi-sheng, LIU Zuo-guang, WANG Cui, SHEN Jie   

  1. Department of Tuberculosis,Dalian Tuberculosis Hospital, Dalian116033, China
  • Received:2012-07-16 Online:2012-10-10 Published:2013-01-08
  • Contact: LU Xi-wei

Abstract: Objective  To evaluate the effect of TST and IGRA in the assessment of tuberculosis (TB) group infection, and to explore the optimal strategy on TB group infection.  Methods  513 contacts in an outbreak of TB were divided into 6 groups according to the degree of exposure, the number of contacts in each group with decreasing degree of exposure (from 1 to 6) were 47, 81, 110, 90, 122 and 63 respectively. All contacts were tested by TST and IGRA jointly. Multiple logistic regression statistics was applied to analyse the correlation between Mtb infection criteria (PPD≥10 mm、PPD≥15 mm、PPD conversion and IGRA-positive) and degree of exposure. After exclusion of 40 contacts who were taking preventive treatment, binary logistic regression was used to determine high risk factors for secondary cases (a total of 19 secondary cases). Incidence rates  of different exposure degrees and infection criteria were compared, as well as the evaluation of the pros and cons of various infection control plan.  Results  PPD≥10 mm, PPD≥15 mm, PPD conversion and IGRA-positive  are closely related to the exposure level (6 levels), P<0.05,  OR values were 1.78 (95% CI: 1.14 to 2.78), 1.01 (95% CI: 0.69 to 1.47) and 2.84 (95% CI: 2.01 to 4.01). IGRA-positive (P=0.03,  OR=3.63) and the degree of exposure (P=0.00,  OR=2.77) are high risk factors for secondary cases. Secondary attack rates of high exposure (L1-L2), medium exposure (L3-L4) and low exposure (L5-L6) were 13.3% (13/98), 3.2% (6/190) and 0.0% (0/185) respectively. The secondary attack rate of a high close contact level was higher than the low exposure levels, there was  statistical significance, χ2=29.85,  P<0.05. The incidence rate of IGRA positive group (8.3%,15/180) was significantly higher than that of the IGRA negative group (1.4%,4/293), which was statistically significant, χ2=14.04,P<0.05. For high exposure level (1st level), chemoprevention were provided for all contacts regardless of TST and IGRA results, for other groups contacts with positive IGRA were the objects of preventive treatment, the sensitivity of the prediction of TB was 94.7% (18/19) and specificity was 46.1% (124/269), positive likelihood ratio was 1.8 and negative  likelihood ratio was 0.1, which was in line with the principle of the best benefits.  Conclusion  IGRA in the diagnosis of tuberculosis infection and incidence prediction is better than TST. Degree of exposure and IGRA positive are important references for the development of TB group infection control strategy.

Key words: Tuberculosis,pulmonary/epidemiology, Tuberculosis,pulomary/prevention and control, Tuberculin test, Interferongamma release tests, Communicable disease control