1. Downloaded from oem.bmj.com on November 29, 2010 - Published by group.bmj.com
Pulmonary tuberculosis infection among
workers in the informal public transport sector
in Lima, Peru
Olivia Janett Horna-Campos, Ezequiel Consiglio, Hector J Sánchez-Pérez, et
al.
Occup Environ Med published online November 23, 2010
doi: 10.1136/oem.2009.051128
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OEM Online First, published on November 23, 2010 as 10.1136/oem.2009.051128
Short report
Pulmonary tuberculosis infection among workers in
the informal public transport sector in Lima, Peru
Olivia Janett Horna-Campos,1 Ezequiel Consiglio,2 Hector J Sanchez-Perez,3
´ ´
1 4 1
`
Albert Navarro, Joan A Cayla, Miguel Martı ´n-Mateo
1
Unidad de Bioestadı´stica, ABSTRACT
Facultad de Medicina, Background Because a strong association was observed What this paper adds
´
Universidad Autonoma de between pulmonary tuberculosis (TB) and the use of
Barcelona, Barcelona, Spain
2
´
Escuela de Salud Publica, public transport, increasing with duration of journey, < An association between pulmonary tuberculosis
Facultad de Medicina, a study was carried out to assess infection by and the use of public transport (minibus) has
Universidad de Buenos Aires, Mycobacterium tuberculosis and working conditions previously been shown.
Buenos Aires, Argentina among workers in this sector.
3´
´
Area Academica de Sociedad, < Moreover, the strength of this association
Cultura y Salud, El Colegio de la
Methods A cross-sectional study was conducted increases as trip duration increases.
Frontera Sur, Chiapas, Mexico between June and September 2008. A total of 104 < We have observed an association between
4
Servicio de Epidemiologı´a, workers from two public transport minibus (‘combi’) positive tuberculin skin test results and the poor
` ´
Agencia de Salut Publica de cooperatives covering marginal areas of the Ate-Vitarte
Barcelona, CIBER de working conditions of minibus workers in
district in Lima were interviewed. Demographic and a precarious occupational setting, characteristic
´a ´
Epidemiologı y Salud Publica,
Barcelona, Spain occupational details were collected as well as prior of low-income countries with high tuberculosis
family and personal history of TB and BCG vaccination. prevalence.
Correspondence to The tuberculin skin test (TST) was administered to each < Minibus workers in such countries should
Olivia Janett Horna-Campos, study subject and an induration of $10 mm was therefore be included in occupational health
Unidad de Bioestadı´stica, Grupo
GRAAL, Facultad de Medicina,
considered positive. Statistical analysis was based on programs.
Edificio M, Campus UAB, logistic models, ORs and their 95% CIs.
Cerdanyola del Valles, 08193 Results TST results were obtained for 70.2% (n¼73), of
Barcelona, Spain; whom 76.6% (n¼56) were positive. Positivity was
ohornac@yahoo.es significantly associated with those who had worked for The objective of this study was to evaluate the
OJH-C, EC, HJS-P, AN and more than 2 years (crude OR 11.04; 95% CI 3.17 to risk of Mycobacterium tuberculosis infection in public
MM-M are members of GRAAL 38.43) and more than 60 h/week (crude OR 9.8; 95% CI transportation workers in the Ate-Vitarte district in
`
(Grups de Recerca d’America i 2.85 to 33.72). These associations remained significant Lima, a marginal area with high PTB prevalence.
`
Africa Llatines; http://www. in a multivariate model as well.
graal.uab.cat/about.html). Conclusion The association observed between years of
Accepted 23 June 2010 working and weekly work burden among minibus MATERIAL AND METHODS
workers suggests an occupational risk in service jobs in Based on a previous study design in the trans-
low-income countries with high TB prevalence. portation setting,2 two minibus cooperatives were
Consequently, other types of users are at increased risk selected from 14 operating services to the study
for TB infection, with a causal relationship between area. A total of 106 workers, 50 drivers and 56 fare-
effect and duration of exposure. collectors over 15 years of age, volunteered and
were included. They were fully informed of the
objectives of the study and of the opportunity to
enrol in a TB program when appropriate. Two
INTRODUCTION workers undergoing active TB treatment were
Smear-positive pulmonary tuberculosis (PTB) is excluded from the study and there were no refusals.
a major public health problem due to its trans- The remaining 104 study participants were
mission within the community. A person with interviewed at central bus stations. Demographic
untreated smear-positive PTB can infect 10e15 and occupational data were collected, including age,
people each year.1 Even when the transmission sex, years of employment in the transportation
pattern is known, in most South American coun- sector, hours worked per day, number of days
tries only household contacts are screened with no worked per week, and personal and family history
screenings in work locations. Public transportation of TB.
is a documented setting where people are exposed At the time of the interview, each subject was
to TB infection and other airborne pathogens, administered the tuberculin skin test (TST) in
particularly in countries with a high prevalence of accordance with the Peru Tuberculosis Program,
PTB.2e4 The urban public transportation services in following the standard Mantoux technique1
Peru, as in other South American countries, have consisting of an intradermal injection of purified
inadequate environmental conditions and a high protein derivative (PPD-RT 23 SSI 2UT (0.1 ml);
risk of airborne pathogens. Vehicles are frequently Statens Serum Institut, Copenhagen, Denmark;
over-crowded, regulations on the length of the obtained from the Peruvian National Institute of
working day are ignored and break times are not Health).1 Indurations were measured 48e72 h after
taken. Thus, overcrowding and increased worker administration and those $10 mm were considered
exposure times represent an occupational risk. positive.5e8 Duration of employment was grouped
Horna-Campos OJ, Consiglio E, author´(orHJ, et al. employer) 2010. Produced by BMJ Publishing
´
Copyright Article Sanchez-Perez their Occup Environ Med (2010). doi:10.1136/oem.2009.051128 Group Ltd under licence. 3
1 of

3. Downloaded from oem.bmj.com on November 29, 2010 - Published by group.bmj.com
Short report
into 0e2 years and more than 2 years.5 Regarding exposure time, DISCUSSION
the number of hours worked per week was calculated based on The validity of the TST is controversial because of its low
scheduled services and information from the Ministry of sensitivity and specificity, lack of reactivity due to immunolog-
Transportation on vehicles, drivers and fare-collectors, and then ical depression, and cross-reactions with other mycobacterial
categorised into more or less than 60 h per week.9 It was esti- species.11 There are also some limitations to using it in adult
mated that workers worked an average of 12 h per day, 5 days populations in countries with high TB prevalence, such as Peru.
per week, exceeding the working hours officially established in However, it is still the most common technique for diagnosing
Peru for all occupations (8 hours per day or 40 hours per week). TB infection,5 even among BCG-vaccinated populations,12
The study was approved by the Ethics Committee of Health because of its easy application and interpretation, and low cost.13
Directorate IV (East Lima), Ministry of Health. The use of public transport was found to be a risk factor for
PTB infection in a previous study conducted in the same
Statistical analysis geographical area,2 in which journey duration was used to assess
A sample size was calculated to obtain 10% precision of the exposure. This theoretical framework led to our hypothesis that
estimated proportion of 60% of positive TSTs10 (n¼92) similar findings would be observed among subjects considered
(a¼0.05). Subjects were chosen from only two companies so exposed to TB infection because they worked as minibus
that all workers in both companies could be studied (n¼104). (combi) drivers and fare-collectors.
Subsequently, we included participants who returned within the Among the study population, 93.2% had arm scars
stipulated time for the TST reading. A sub-study of non- compatible with prior BCG vaccination. Given the character-
responders was conducted using two-sided t tests for mean istics of the Peruvian TB Prevention Program and the mean age
contrasts and exact tests of proportions to detect possible biases. of the subjects, we calculated that they were vaccinated more
Univariate and bivariate analyses, as well as a multivariate than 15 years ago (including those re-vaccinated after 6 years)
logistic model, were preformed. ORs and 95% CIs were calcu- and thus it is unlikely prior vaccination influenced TST
lated. Data were analysed using SPSS v 15. results.13 Moreover, the association between occupational
characteristics and M tuberculosis infection, adjusted for age,
RESULTS provides a specific epidemiological profile given these working
A total of 104 workers were interviewed and administered a TST, conditions: an informal work setting, lack of a job contract,
and of these 73 (70.2%) returned for the TST reading, of whom lack of fixed break times, no health insurance and no health
56 (76.6%; 95% CI 66.9% to 86.3%) were TST positive. benefits.
The mean (SD) age of the 73 who returned for the test reading In this context, the response rate obtained was optimal and
was 33.9 (9.1) years. None had a known history of TB, although perhaps linked to health concerns among these workers (data
three (4.1%) were uncertain. Nine (12.3%) stated they had not shown). The high rate of TST positivity of 76.6% (95% CI
a close relative with TB. Arm scars compatible with prior BCG 66.9% to 86.3%) was higher than the results observed in contact
vaccination were found in 68 (93.2%) subjects. tracing studies (55e61%)10 and suggests high exposure in this
The 31 who did not return for the test reading were not setting.
significantly different from responders with regard to age (mean Furthermore, the prolonged daily and weekly exposure
30.1 years), BCG (87%), family history (9.7%), years in the job suggests that the association is not coincidental and that
(64.5%) or hours worked per week (48.4%). a worker with active PTB is a transmission source for passengers.
Fifty-one subjects (69.9%) had worked in public trans- Despite AFB+ TB presentation, some workers continue
portation for more than 2 years and 50 (68.5%) worked more working, as shown by the two employees excluded from the
than 60 h per week. study, or may default from anti-TB treatment when signs and
According to the bivariate analysis, no association was found symptoms have minimised14 or because of incompatibility
between a positive TST and a family history of TB (Fisher exact between their working hours and those of health centres.
test, p¼0.105). A positive TST was found to be associated with Therefore, minibus workers and companies should be targeted
more than 2 years of employment (OR 11.04; 95% CI 3.17 to for specific and effective preventive interventions within occu-
38.43) and with working more than 60 h per week (OR 9.8; 95% pational health programs.
CI 2.85 to 33.72). When controlling for age using a logistic The characteristics revealed in our study show that there is
multivariate model, the following were associated with a posi- a risk of infection among urban transportation workers in cities
tive TST result: more than 2 years of employment (adjusted OR with high TB prevalence. Furthermore, one must consider the
15.6) and working more than 60 h per week (adjusted OR 12.7) repercussions for passengers. This association must be inter-
(table 1). preted in the context of working and environmental conditions.
Table 1 Predictive factors for tuberculin skin test positivity in workers in the informal public transport
sector, Lima, Peru
Variable TST+ n/N (%) Crude OR 95% CI Adjusted OR by age 95% CI
Time in job
#2 years 10/22 (45.5) 1 1
>2 years 46/51 (90.2) 11.04 3.17 to 38.43 15.66 3.25 to 75.35
Hours/week
#60 h 11/23 (47.8) 1 1
>60 h 45/50 (90.0) 9.8 2.85 to 33.72 12.7 2.72 to 49.45
Age 1.02 0.96 to 1.08 1.06 0.98 to 1.15
Reference categories: #2 years in job and #60 h/week.
TST, tuberculin skin test.
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Horna-Campos OJ, Consiglio E, Sanchez-Perez HJ, et al. Occup Environ Med (2010). doi:10.1136/oem.2009.051128

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Short report
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with increased circulation of resistant mycobacteria, such as tuberculosis. A two-years study of contagion in a tuberculosis ward. Am J Hyg
1959;70:185e96.
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extremely drug-resistant TB strains.14 2002).
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Relacion de unidades de transporte por ruta. Lima: Gerencia del Transporte Urbano.
´ ´
Funding This work was funded partly by the Fundacion Autonoma Solidaria (FAS-UAB) http://www.gtu.munlima.gob.pe/Internet_Web/Transporte_Publico/Empresa_Ruta.
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