[Factors predicting new tuberculosis infections and tuberculin conversions in a contact tracing system]. / Factores predictores de la aparición de nuevos casos de infección tuberculosa y de viraje tuberculínico en un estudio de contactos.

OBJECTIVE: To study new cases of latent tuberculosis (TB) infection, active TB and tuberculin conversions detected by means of a system for tracing the contacts of TB patients and to analyze the factors that predict the appearance of new cases. METHOD: We performed a longitudinal, prospective study of all contacts of patients with active TB in the health district of Vigo, Pontevedra, in 2005 and 2006. The total rate of positive tuberculin test results and the percentage of tuberculin conversions at the end of the study were analyzed. The predictive factors for positive results were identified by a multivariate analysis. RESULTS: A total of 742 contacts of patients with TB were studied. The mean age of contacts was 35 years (SD=19.1) and 406 (54.7%) were women. Most (91.8%) were contacts of pulmonary TB patients, 70.4% were contacts of bacilliferous patients and 40.2% were highly exposed. The study was completed with 540 (72.8%) cases, 280 (51.9%) of which were infected or diseased. Of the 297 contacts who completed the study 12 weeks later, 37 (12.5%) showed tuberculin conversion. The factors independently associated with a positive tuberculin test result were male sex, age >or= 30 years old, and degree of contact (high exposure in contacts and positive sputum smear in the index case); the two latter factors were predictive for tuberculin conversion. CONCLUSION: Contact tracing of TB patients was an effective strategy in our area. The factors most closely related to positive tuberculin test results, particularly to conversion, were positive direct microscopy of sputum for the index case and high exposure. Strategies to improve adherence to this kind of study should be sought.

Factores predictores de la aparición de nuevos casos de infección tuberculosa y de viraje tuberculínico en un estudio de contactos / Factors predicting new tuberculosis infections and tuberculin conversions in a contact tracing system

Objetivo. Examinar la aparición de nuevos casos de infección tuberculosa latente, tuberculosis activa y virajes tuberculínicos detectados mediante un estudio de contactos (EC) de pacientes con tuberculosis (TB) y analizar los factores que predicen su aparición. Método. Estudio prospectivo, longitudinal, que incluyó a todos los contactos de casos con TB activa del área sanitaria de Vigo (Pontevedra) durante 2005 y 2006. Se analizó la tasa total de pruebas de tuberculina (PT) positivas y el porcentaje de virajes tuberculínicos al final del EC. Mediante un análisis multivariante se observó cuáles fueron los factores predictivos de dichos resultados. Resultados. Se estudiaron 742 contactos de pacientes con TB, con una edad media de 35 (desviación estándar = 19,1) años, 406 (54,7%) mujeres. El 91,8% fue contacto de enfermos con TB pulmonar, el 70,4% contacto de enfermos bacilíferos y el 40,2% tenía contacto íntimo. Completaron el estudio 540 pacientes (72,8%), de los cuales estaban infectados o enfermos 280 (51,9%).De los 297 que completaron el estudio a las 12 semanas, 37 (12,5%) presentaron un viraje tuberculínico. Los factores que se asociaron de forma independiente con un resultado positivo de la PT fueron el sexo masculino, la edad $ 30 años y la intensidad del contacto íntima por parte de los contactos, y la baciloscopia positiva por parte del caso índice, siendo estos 2 últimos factores los que predicen la conversión. Conclusión. El EC de enfermos con TB es una estrategia eficaz en nuestro medio. Los factores que se correlacionan de forma más importante con presentar una PT positiva, sobre todo con la conversión, son la microscopia directa de esputo positiva del caso índice y el contacto íntimo. Es importante buscar estrategias que permitan mejorar la adhesión a este tipo de estudios

Objective. To study new cases of latent tuberculosis (TB) infection, active TB and tuberculin conversions detected by means of a system for tracing the contacts of TB patients and to analyze the factors that predict the appearance of new cases. Method. We performed a longitudinal, prospective study of all contacts of patients with active TB in the health district of Vigo, Pontevedra, in 2005 and 2006. The total rate of positive tuberculin test results and the percentage of tuberculin conversions at the end of the study were analyzed. The predictive factors for positive results were identified by a multivariate analysis. Results. A total of 742 contacts of patients with TB were studied. The mean age of contacts was 35 years (SD = 19.1) and 406 (54.7%) were women. Most (91.8%) were contacts of pulmonary TB patients, 70.4% were contacts of bacilliferous patients and 40.2% were highly exposed. The study was completed with 540 (72.8%) cases, 280 (51.9%) of which were infected or diseased. Of the 297 contacts who completed the study 12 weeks later, 37 (12.5%) showed tuberculin conversion. The factors independently associated with a positive tuberculin test result were male sex, age $ 30 years old, and degree of contact (high exposure in contacts and positive sputum smear in the index case); the two latter factors were predictive for tuberculin conversion. Conclusion. Contact tracing of TB patients was an effective strategy in our area. The factors most closely related to positive tuberculin test results, particularly to conversion, were positive direct microscopy of sputum for the index case and high exposure. Strategies to improve adherence to this kind of study should be sought