the study was conducted in the ate - vitarte district ( population 365,473 ) , which is located 12 km from the center of lima .
it is a marginal urban area that receives immigrants who come to lima with high rates of tb .
the study was reviewed and approved by the ethics committee of the east lima health directorate iv . during july 
august 2004 , interviews were conducted with a random sample of 150 commuters > 15 years of age who had productive coughs for > 15 days and who came to health services for treatment .
a total of 142 persons agreed to participate : 96 were treated at hospitals and 46 were treated at health centers .
we obtained demographic and socioeconomic information , as well as information on perceived health , and means of transportation used in commuting .
all persons with productive coughs were requested to provide 3 sputum samples ( the first immediately after the interview and the other 2 on 2 consecutive days ) for smear testing .
samples were tested by using the ziehl - neelsen method , which is used in all epidemiologic surveillance in peru ( 11 ) .
study participants were considered positive for pulmonary tb if > 1 acid - fast bacilli ( afb ) were found ( 11 ) .
results were analyzed by using bivariate and multivariate logistic models with spss version 12 software ( spss inc .
seventeen ( 11.9% ) of 142 study participants were smear positive ( 29.6% 1 cross , 41.0% 2 crosses , and 29.4% 3 crosses ) .
two persons had been discharged from a tb treatment program < 6 months earlier . * more than 3 persons sleeping in the same room
* afb , acid - fast bacilli ; or , odds ratio , ci , confidence interval . none of the demographic and socioeconomic indicators analyzed ( table 1 ) were associated with pulmonary tb .
the use of a minibus and a commuting time > 1 hour had the highest associations with pulmonary tb .
adjusted relationships obtained by logistic regression that controlled for all variables shown in table 2 confirmed that commuting to work by minibus was associated with a positive test result for pulmonary tb ( adjusted odds ratio 4.90 , 95% confidence interval 1.0423.04 ) .
we observed a pulmonary tb prevalence rate of 12% in persons with chronic productive coughs who came to health services in the study area .
this rate was similar to a prevalence of 11% reported in a similar study conducted in an area of poor socioeconomic status in chiapas , mexico ( 12 ) .
the proportion of persons 1544 years of age with pulmonary tb in our study was consistent with data of the world health organization and the peruvian ministry of health , which show that this age group has the highest prevalence of this disease ( 5,13,14 ) .
our results also showed that there were no sex - related differences in the frequency of pulmonary tb ( 13 , 14 ) .
however , this finding should be interpreted cautiously because of the small sample size , particularly the number of persons who lived in extreme poverty .
another factor that could limit our conclusions is accessibility of persons in areas of extreme poverty to public transportation .
the fact that the field work phase of our study could not be increased because of shortages of resources and health center personnel time is also a limitation .
the relationship of having pulmonary tb with working at home or away from home showed a positive prevalence ratio of 6.06 . among persons working outside the home , commuting by minibus increased the risk of having pulmonary tb by a factor of 4.09 compared with persons who used individual forms of transportation . a commuting time > 1 hour on a minibus also increased the risk for pulmonary tb by a factor of 2.07 ( table 2 ) .
minibuses in lima increase the risk for pulmonary tb because they are usually overloaded ( capacity is often doubled ) in the early morning and late evening .
overcrowding , exposure to persons with productive coughs while commuting 2 times a day 5 days a week , and closed windows on minibuses , combined with a high prevalence of pulmonary tb in lima , increase the risk of acquiring this disease . because persons with cases of pulmonary tb have more productive coughs in the morning ( when more bacilli are released because of their accumulation at night ) ,
there is increased risk for transmission of tb to other passengers ( 15 ) , as has already been suggested by other studies in developing and industrialized countries ( 69 ) .
the findings that 41% of persons tested were positive with 2 crosses and 29.4% were positive with 3 crosses indicate poor tb prevention and control programs in the study area and higher probabilities of transmission ( 15 ) . despite the limitations of our study , commuting in minibuses was a risk factor for pulmonary tb .
consequently , preventive measures need to be taken by health services to encourage persons with productive coughs to avoid this type of public transportation and to come to health services for diagnosis and treatment .
health services should also be more accessible to persons with pulmonary tb who , for whatever reason , can not use other forms of transportation .
 the association between public transportation for commuting and pulmonary tuberculosis ( tb ) was analyzed in workers in lima , peru . 
 traveling in minibuses was a risk factor for pulmonary tb . 
 preventive measures need to be taken by health services to prevent spread of this disease . 
The Study
Conclusions