Original article
Extrapulmonary tuberculosis: epidemiology and risk factorsTuberculosis extrapulmonar: epidemiología y factores de riesgo

https://doi.org/10.1016/j.eimc.2011.03.005Get rights and content

Abstract

Objective

To describe the epidemiology and risk factors associated with extra-pulmonary tuberculosis (EPTB).

Method

Cases of tuberculosis (TB) diagnosed from 1991 to 2008 in a Caucasian population were classified as EPTB or pulmonary TB (PTB). Of all cases, 63.7% were followed up in a specialist TB unit. A standardised protocol for data collection was used, including: gender, age, BCG vaccination, contact with PTB patient, smoking habit, alcohol abuse, diabetes mellitus, immunosuppressive drugs/steroids and HIV-status. These variables were compared between EPTB and PTB groups. Statistical analysis was based on logistic regression. Odds ratios (OR) and their 95% confidence intervals (CI) were calculated.

Results

Among the 2,161 cases diagnosed, 1,186 were PTB and 705 EPTB. The overall TB incidence had fallen from 79.9/100,000 in 1992 to 27.1/100,000 in 2008, P<.05. The number of EPTB cases decreased more slowly than PTB. EPTB increased from 30.6% of cases in 1991-1996 to 37.6% in 2003-2008 (lymphatic site increased 27%), by trend test P<.05. At multivariate level, being female (OR 2.04; 95% CI: 1.56-2.66) and age (OR 1.02; 95% CI: 1.01-1.022) were associated with EPTB, while alcohol abuse (OR 0.33; 95% CI: 0.20-0.52), smoking habit (OR 0.45; 95%CI: 0.34-0.59), contact with PTB patients (OR 0.57; 95% CI: 0.44-0.76) and BCG vaccination (OR 0.64; 95% CI: 0.44-0.92) had a protective effect. The proportion of female gender and age of patients increased over time, whilst there was a decrease in BCG vaccinated patients.

Conclusions

Whilst there has been a reduction in the overall incidence of TB, the proportion of EPTB increased. The proportional increase in EPTB could be explained by an increase in life expectancy and the predominance of women in the population, and by a decline in BCG vaccinated patients.

Resumen

Objetivo

Conocer la epidemiología y los factores de riesgo asociados con la tuberculosis extrapulmonar (EPTB).

Método

Los casos de tuberculosis (TB) diagnosticadas entre 1991-2008 en una población caucásica fueron clasificados como EPTB o TB pulmonar (PTB). De todos los casos, 63,7% fueron seguidos en una consulta monográfica de TB. Se utilizó un protocolo estandarizado para la recogida de los datos, incluyendo: sexo, edad, vacunación con BCG, contacto con algún paciente con PTB, tabaquismo, alcoholismo, diabetes mellitus, corticoides/fármacos inmunosupresores e infección por el VIH. Se compararon las variables entre los grupos de EPTB y de PTB. El análisis estadístico se basó en un estudio de regresión logística. Se calcularon los odds ratio (OR) y sus intervalos de confianza (IC) del 95%.

Resultados

Entre 2.161 casos diagnosticados, 1.186 fueron PTB y 705 EPTB. La incidencia global de TB disminuyó desde 79.9/100.000 en 1992 hasta 27.1/100.000 en 2008, p<0,05. El número de casos de EPTB disminuyó de forma más lenta que el de PTB. La proporción de EPTB aumentó desde 30,6% de los casos en 1991-1996 hasta 37,6% en 2003-2008 (la localización ganglionar aumentó un 27%), p<0,05 en un ji al cuadrado de tendencia. En el estudio multivariante, ser mujer (OR 2,04; IC 95%: 1,56-2,66) y la edad (OR 1,02; IC 95%: 1,01-1,022) se asociaron con EPTB mientras que el alcoholismo (OR 0,33; IC 95%: 0,20-0,52), el tabaquismo (OR 0,45; IC 95%: 0,34-0,59), el contacto con pacientes con PTB (OR 0,57; IC 95%: 0,44-0,76) y la vacunación con BCG (OR 0,64; IC 95%: 0,44-0,92) tuvieron un efecto protector. La proporción de mujeres y la edad de los pacientes aumentaron a lo largo del tiempo, y descendió el número de pacientes vacunados con BCG.

Conclusiones

Con la reducción en la incidencia global de TB, la proporción de EPTB aumentó. El incremento proporcional de la EPTB se podría explicar por el aumento de la esperanza de vida y el predominio de la mujer en la población, y por un descenso de los pacientes vacunados con BCG.

Introduction

There has been a constant decrease in the number of cases of tuberculosis (TB) in industrialised countries due to improvements in social conditions and the availability of effective antituberculosis drugs.1 This decrease halted between the years 1985 and 1992 due to the relaxation of prevention and control programs, the appearance of HIV infection, and the migratory movements of people from countries with a greater incidence of TB.2, 3 Although the total number of cases of TB has decreased, the reduction in cases of extra-pulmonary tuberculosis (EPTB) has been smaller, resulting in a proportionate increase in EPTB compared to pulmonary tuberculosis (PTB).4 In the cases of TB reported in the US, for example, EPTB accounted for 15.7% of total cases in 1993, but 21% in 2006.5 The reasons for this smaller reduction are little known and have been attributed, among others causes, to demographic changes in the susceptible population and a decreased uptake of vaccination with BCG.6, 7 There are no prospective studies that analyse other possible enhancing factors for EPTB infection.

We present a prospective research study with the following targets:

  • 1.

    To describe the epidemiology of EPTB in a Caucasian population, comparing the incidence and characteristics of EPTB with those of PTB.

  • 2.

    To analyse factors contributing to the increased proportion of cases of EPTB.

Section snippets

Method

A specialised unit for following up patients with TB was opened within our hospital in 1991, and a program for prevention and control of TB began in the North West Spanish region of Galicia in 1995. An active search of all the diagnosed cases of TB was performed from 1991 in our health area with a predominantly Caucasian population. In 1991 the population consisted of 218,749 inhabitants, with a mean age of 38.8 years (16.3% older than 64 y); 51.% women (59.9% older than 64 y); 0.29% were born

Results

A total of 2,161 cases of TB were diagnosed. Five (0.23%) cases were in patients born outside Spain. The incidence decreased over time from 79.9 per 100,000 in 1992 (sputum smear-positive 26.3) to 27.1 per 100,000 in 2008 (sputum smear-positive 10). Among the total of 2,161 cases, 705 (32.6%) were EPTB, 1,186 (54.9%) were PTB, 106 (4.9%) were disseminated TB, and 164 (7.6%) were concurrent EPTB-PTB. The number of cases of both EPTB and PTB decreased over time, but EPTB cases decreased more

Discussion

Our data confirms a lower reduction in EPTB compared with the reduction in PTB, in an area with intermediate incidence of TB, a good program for prevention and control of the TB, and predominantly Caucasian population where life expectancy and the proportion of women in the population are increasing. All the diagnosed cases of TB have been reported and the lower reduction in EPTB cases is not due to an increase in the reporting of cases or as a result of over-diagnosis, since the percentage of

Conflict of interests

The authors declare no conflicts of interest related to this study.

Acknowledgments

The first author had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

We would like to thank Ana Del Rio, Consultant Paediatrician, Royal Blackburn Hospital, East Lancashire, United Kingdom, for revision of the translation to English.

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