Incidence of Latent Tuberculosis Infection in a study of household contacts treated in a General Hospital of the City of Buenos Aires

ABSTRACT

Introduction: The study of household contacts of patients with tuberculosis (TB) is an essential strategy for the early diagnosis of latent tuberculosis infection (LTBI) and for the establishment of the corresponding treatment for the purpose of reducing TB prevalence in the population. Objective: To know the incidence of LTBI in household contacts and the degree of compliance with control studies and chemoprophylaxis (ChP). Materials and Methods: We carried out a retrospective analysis of > 15-year-old household contacts of patients with TB treated in the Hospital General de Agudos Parmenio Piñero between January 2016 and February 2018. Chest x-ray and tuberculin skin test (PPD, Purified Protein Derivative) were requested, considering ≥ 10 mm as a positive cut-off point. The tuberculin skin test was repeated after 3 months in subjects with negative results. ≥ 5 mm was also considered as PPD+ when analyzing the data. The cases in which patients followed > 80% of the indicated regime were considered as compliant with ChP 3 months of isoniazid in primary ChP and 6 months in secondary ChP. Results: 4 (1.2%) of the 344 admitted contacts were diagnosed with TB through chest x-rays with pathological images. These 4 contacts with TB were excluded from the study. Within the remaining 340 subjects, with a mean age of 35 ± 16 years, there were 154 (45%) males, 180 (52%) Argentinians and 144 (43%) Bolivians. Of the 193 (57%) subjects who complied with the performance of the basal PPD test, 38 (20%) showed PPD ≥ 10 mm and 89 (46%) ≥ 5 mm. Women were more compliant than men with PPD testing 122 out of 186 (55%) vs. 71 out of 154 (45%); p = 0.005. There was no significant difference as regards age and nationality. Only 33 (21%) patients complied with the performance of the second PPD test, without any conversions for the 10 mm cut-off point, and with 3 conversions considering ≥ 5 mm as PPD+. Primary ChP was indicated to 55 patients, and secondary ChP to 38 patients. The compliance rate was 75% and 39%, respectively, without a significant association with age, gender or nationality. No adverse event associated with isoniazid was reported. Conclusion: We found 20% LTBI within the population under study considering ≥ 10 mm as PPD+; 46% was found with ≥ 5 mm PPD. There was a low level of compliance with the performance of the PPD test (though it was higher in women) and of secondary ChP.