ASSOCIATION BETWEEN
PULMONARY TUBERCULOSIS
AND SMOKING : A CASE
CONTROL STUDY
Talha Saad 1, Jyoti Markam 2
1.Department of Respiratory Medicine ,Bundelkhand Medical College,Sagar, Madhya Pardesh
2.Department of Community Medicine , Bundelkhand Medical College,Sagar, Madhya Pardesh
Abstract
Background: Tuberculosis (TB) is a key public health problem among population of
Sagar district in Madhya Pradesh state, central India. However, there is no any detailed
study undertaken to find out the risk factors associated with the development of TB
disease in this community. A case controlled study was conducted among population in
Sagar district of Madhya Pradesh to find out association with smoking and tuberculosis.
Methods : A total of 111 sputum smear positive patients of pulmonary tuberculosis and
333 controls matched for age and sex were interviewed according to a predesigned
questionnaires .
Results: The adjusted odd ratio of the association between tobacco smoking and
pulmonary tuberculosis was 3.8 (95% CI 2.0 to 7.0 p value < .0001). A positive
relationship between pack year, BMI and socioeconomic class was also observed.
Conclusion: The study has demonstrated strong association between smoking and
tuberculosis. We need to supplement the efforts in advocacy, communication and social
mobilization for reducing the smoking in the community for effective control of
Tuberculosis.
Address for corrospondence:
Dr Talha Saad
Department of Respiratory Medicine, Bundelkhand Medical
College,Sagar,MP,470001
dr.talhasaad@gmail.com
Introduction
India is classified along with the sub-Saharan African countries to be among those
with a high burden and the least prospects of a favourable time trend of the disease as of
now (Group IVcountries). The average prevalence of all forms of tuberculosis in India is
estimated to be 5.05 per thousand, prevalence of smear-positive cases 2.27 per thousand
and average annual incidence of smear-positive cases at 84 per 1,00,000 annually. (1).
The World Health Organization has set a goal to lower annual TB incidence to less
than one case per million by 2050 (1). Although the current approach to TB
control focuses on case detection and treatment, recent studies suggest that
this strategy might not be sufficient to achieve this goal and it may also be
necessary to reduce risk factors that contribute to the occurrence of tuberculosis
infection and/or disease (2, 3). Such risk factors may act at one of several steps in
the natural history of the disease.
Susceptible individuals become infected with Mycobacterium tuberculosis after
exposure to a person with active pulmonary tuberculosis. Once infected,
individuals either develop disease within the first 1 to 2 years of infection, referred
to as primary disease, or go on to develop a latent asymptomatic infection, which
can progress to active disease sometime during that individual’s life.
A first step toward this goal is to better understand the effects of modifiable
risk factors, including tobacco smoking, on any of these steps that could
ultimately increase the occurrence of TB.
An estimated 1.3 billion people smoke tobacco products, the majority of whom
live in low- or middle-income countries where the burden of TB is also
concentrated (4). Several systematic reviews and meta-analyses of observational
studies have pointed to a positive association between tobacco smoking and active
TB disease (5-7).
Several large observational studies also reported an increased mortality from TB
among smokers but these studies did not provide direct evidence on smoking and
the incidence of active TB (8-10).A few cohort studies have reported a positive
association between smoking and active TB (11-14). However, these cohort studies
might not have yielded generalized results because they were conducted in highrisk populations such as gold miners (11), patients with silicosis (12,13), and the
elderly (14).
We report here a population survey conducted in Sagar District, Madhya Pradesh that
provides evidence that smoking may increase the risk of tuberculosis . We did one year
epidemiological research in the study population.
METHOD AND MATERIAL:-
Case control study was conducted at Sagar district , Madhya Pradesh India. All the
pulmonary tuberculosis cases registered in Outpatient of Bundelkhand Medical College
Sagar ( n=165). The controls (n=333) were subjects without respiratory disease. All
controls were subjected to clinical evaluation, chest radiograph and sputum examination.
All subjects with co morbid conditions such as diabetes mellitus, human deficiency virus
infection, malignancy and those on any immunosuppressive drugs were also excluded
from study.
The total number of registered cases in the Outpatient were 165. In this study 125 cases
were completely approachable and rest of cases 40 are not found due to incomplete
addresses , wrong addresses, migrate from city or death of patient. Out of 125 cases only
111 cases agree for interview and rest of 14 cases not given consent for interview.
Matching factors was age ± 5 years , sex and socioeconomic status. In person interview
of each case and control was taken using a pretested structured questionnaire enquiring
about smoking history, household smoke exposure , environmental smoke exposure ,
tobacco chewing ,alcoholism, housing characteristics and score on modified Prasad
socioecomonic status scale was used for data collection. This scale takes account of per
capita income of the family to classify study groups into Upper high ,High, Upper
middle, Lower middle,and Poor socioeconomic status.
Detail of smoking were noted carefully with regard to type , current smoking status, age
of starting smoking , duration of smoking , quantity of smoking. In this study somking
was defined as having ever smoked for at least 5 years. The number of pack year smoked
was calculated as the average number of bidi smoked per day multiplied by the duration
of smoking divided by 20.
Result:A total of 111 patients and 333 controls were enrolled in the study. Smoking history was
present in 33.3% of patients as compared to 13.8% of controls. The mean pack /year were
4.77 among patient and 0.88 among controls. The odd ratio of developing pulmonary
tuberculosis among smoker was 3.8 times more than that nonsmokers [ odd ratio =3.8
(95%CI 2.0 to 7.0) p<0.001]
The odd ratio of developing pulmonary tuberculosis among person who smoked for a
duration of >5 years [ adjusted odd ratio= 5.7 [95% CI 2.4 to 13.1] was more in
comparison to person who smoked for a duration of <5years [ adjusted odd ratio= 2.5
[95% CI 1.1 to 5.7]
Analysis were also done to assess the association between pulmonary tuberculosis and
various factors like socioeconomic status, BMI, type of housing and alcohol intake.
The odds of developing pulmonary tuberculosis among social class V [ adjusted odd ratio
=5.3( 95% CI 1.8 to 16.0]was more than that among social class IV [ adjusted odd ratio=
2.3 (95% CI 0.8 to 6.7] with reference to social class type III.
Alcohol intake was also found to have an association with the occurrence of pulmonary
tuberculosis [adjusted odd ratio=1.7( 95% CI 0.9 to 3.3)]
BMI < the median valve of 19.4 was strongly associated with pulmonary tuberculosis[
adjusted odd ratio =4.1( 95% CI 2.5 to 6.8)]
Person living in kuccha or semipukka houses [ adjusted odd ratio=3.2[ 95%1.4 to 7.5)]
had almost similar odds of developing pulmonary tuberculosis when compared with
person living in pucca houses [ adjusted odd ratio =2.3 (95% CI 1.6 to 5.6)].
Table 1: Association of pulmonary tuberculosis and smoking
variables
cases
controls
matched
(111)
(333)
odd ratio
(95% CI)
adjusted
odd ratio
(95% CI)
p value
Duration of
smoking
<5 years
15 (13.5)
30 (9.0)
2.0(1.0 to 4.2)
2.5(1.1 to5.7)
0.03
>5 years
22 (19.8)
16 (4.8)
5.6(2.7 to
11.8)
5.7(2.4 to 13.1)
0.0001
Table 2: Factors associated with pulmonary tuberculosis
Variables
Matched OR (95%
CI)
Adjusted OR (95%
CI)
p value
>45
2.56(1.84-3.56)
2.51(1.81-3.50)
<0.0001
<45
1.28(0.87-1.89)
1.21(0.77-1.86)
<0.0001
Smoking
3.4 (2.0 to 5.8)
3.8 (2.0- 7.0)
<0.0001
5.3 (1.8 to 16.0)
2.3(0.8 to 6.7)
3.6(1.0 to 12.8)
1.9 (0.6 to 6.4)
0.04
0.3
3.2 (1.4 to 7.5)
2.8(1.1 to 7.2)
0.03
semipucca
Body mass index
2.3 (1.0 to 5.1)
4.1(2.5 to 6.8)
2.3(0.9 to5.6)
4.2(2.4 to 7.3)
0.07
<0.0001
Alcohol
19(17.1)
37(11.1)
<0.0001
Age
Social class
type V
type IV
House type
kuccha
DISCUSSION
This study shows that current or ex-smokers had a higher prevalence of TB than never
smokers and that there was a slightly higher risk for age >45 years.This suggests that the
increased risk of disease and death from tuberculosis among smokers may be due, at least
in part, to an increased risk of smokers becoming infected with M tuberculosis.
Our study confirms previous studies that showed an association between smoking and
tuberculosis infection in at risk groups(11-14) For example, in silicotic patient(12-13)
reported a higher risk of infection among smokers which increased with duration of
smoking. In contrast to previous studies investigating specific high risk groups,(11-14)
the current study is the first to investigate the correlation between smoking and
tuberculosis in a cross sectional population survey in a high incidence community.
The reason for the increased risk of infection in smokers is unclear, but may be explained
by the effects of smoking on pulmonary host defences. Smoking has been shown to
reduce natural killer cytotoxic activity, to suppress T cell function in both lung and blood,
to impair mucociliary clearance of particles, and to increase numbers of alveolar
macrophages in the lower respiratory tract. Cells of the macrophage-phagocytic group
influence immediate or innate immunity through their handling and elimination of
mycobacteria, and products of cigarette smoke may therefore favour persistence and/or
replication of ingested mycobacteria by impairing the macrophage or dendritic cell
function. (15)
To take possible sources of bias into account we have considered the following. Men and
persons in the highest income category are under-represented, but this is unlikely to be of
significance as neither sex nor income was a confounder for the association between
smoking and positive sputum for AFB.
A weakness of the study is that we did not test the HIV status of participants and were
therefore not able to correct for HIV status. Confounding factors that were taken into
consideration were individual monthly income, BMI, and education level. However, we
cannot entirely discount the possibility that socioeconomic and behavioural differences
other than smoking may have affected the relationship between smoking and tuberculous
.
Although our evidence suggests that tobacco smoking is only a moderate risk factor in
TB, the implication for health in this rural population is critical. Because tobacco
smoking is quite prevalent, a considerable portion of TB may be attributed to tobacco
smoking . More importantly, this association implies that smoking cessation might
provide benefits for TB control in this rural population. There is an urgent need to
develop and implement culturally appropriate awareness raising activities to target
smoking to support the efforts to control TB in this community.
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