to 24 hours, depending on a range of factors including physical activity, gender and inhalation intensity. The half-life of CO in a person who breathes regular air is about 5 hours. CO measurement is commonly used in smoking cessation programmes and is also used to evaluate the quality of the air in indoor social places, as it was observed in the study of Waring et al,10 which analysed bars in Austin, Texas, before and after smoking ban. In spite of CO not being speciﬁc of cigarette smoke, in indoor places tobacco smoke is the most important source of CO, as showed by Goniewicz et al11 Their study evaluated secondhand smoke in Polish bars by measuring CO concentration and concluded that the main source of CO is tobacco smoke. Tual et al12 analysed the impact of tobacco control policies on exhaled CO in almost 59 000 non-smokers in 27 European Union countries and noticed a strong link between antismoking poli- cies and the exposure to passive smoking. The mean exhaled CO was 1.6 ppm in Ireland, which has a strong antismoking police, and 6.6 ppm in Greece, without any antismoking police. Some studies13 14 show a strict relation between the CO concentration and the risk of cardiovascular events and have noted a reduction in hospital admissions due to cardiovascular events after smoking-ban laws having been implemented. Despite the evidence of cardiovascular event reduction after smoking-ban laws, few studies have quantiﬁed the reduction of the SHS components, which can justify such events. Here, we have evaluated the CO concentration in hospitality venues and their workers before and after the smoking-ban law. METHODS The ethics committee for Research Project Evaluation (CAPPesq) of the Hospital das Clinicas, School of Medicine, University of São Paulo approved the study. The ﬁrst phase included the period prior to the implementa- tion of the tobacco-free policy (from 23 July to 2 August 2009), and the second phase was performed approximately 12 weeks after the banning law was introduced (from 29 October to 7 November 2009), using the same agents, same places, on the same day of the week, same time of the day and with the same workers as were analysed in the ﬁrst visit. Approximately 100 agents from the Sao Paulo State Center of Surveillance were trained to use a CO monitor, to obtain a signed informed consent and to conduct data collection. They visited bars, restaurants, nightclubs and similar venues collecting data from the environment and from some workers at these places (two smoking and two non-smoking workers whenever possible). They were instructed to apply the informed consent to smoking and non-smoking workers of these venues and then to measure their exhaled CO. Ascertained workers were, pref- erentially, those working in closed spaces of the visited venues. Study sample According to the São Paulo Hotels and Restaurants Syndicate,15 there are more than 30 000 restaurants, bars, nightclubs and similar places in the city of São Paulo. A total of 585 hospitality venues inside the city of São Paulo were visited before and after the tobacco-free policy was implemented. The sites were a sample of convenience. They were selected over a geographical range of the city, sampled from a large number of entertainment establishments in all ﬁve geographical zones: north, east, south, west and centre. The measurement of CO was done indoors, in partly closed spaces (semi-open), and in open spaces of the venues. The CO measurement of open areas was done in front of the main door of the establishment, keeping a close contact with Tobacco Control 2011;20:156e162. doi:10.1136/tc.2010.037614 Research paper the indoor area. The samples were obtained during the busiest period of the weekdon Thursdays, Fridays or Saturdays between 21:00 and 03:00. Measurements of exhaled air in venue workers, smokers or not, were also done. Only workers in good health were invited to participate in the study, and all of them provided written informed consent. We planned to get at least one smoker and one non-smoker from every establishment. They were ques- tioned about their smoking status (non-smoker, have never smoked or is an ex-smoker (without smoking for at least 30 days); eventual smoker, have smoked at least one cigarette in the last 30 days; regular smoker, smoke every day), mean number of cigarettes smoked per day, sex and age. CO monitors The samples were collected with two types of portable CO measuring devices. The monitors use a sampling method that channels the gas sample directly over the sensor during the test. This ensures that the electrochemical sensor is exposed to the gas sample for the required length of time to give an accurate reading. The electrochemical sensor is designed to react to the presence of carbon monoxide and produces an output current proportional to the level of CO. This is then read by the microprocessor and converted to display the equivalent parts per million (ppm). The ﬁrst monitor used was the ToxCo (Bedfont Scientiﬁc; Rochester, England), a small portable device to measure environmental CO concentration, which has a display with two numbersdthe ﬁrst one shows the CO measure on real time and the second one shows the highest level achieved in the present measure. The second one was the PiCo (Bedfont Scien- tiﬁc; Rochester, England), which has a similar mechanism as the ToxCo, but measures exhaled human CO concentration. The measures in visited venues were done in real time, and were done in the centre of the establishments, avoiding contamination by ovens. Before starting the test, the person was instructed to hold his/her breath for 15 seconds and then exhale slowly into the mouthpiece. They were calibrated according to manufacturer ’s instruction. The CO monitors are certiﬁed by The National Physical Laboratory of the UK. Data collected from venues were compared with data obtained by the CETESB in nine automatic stations located in different parts of São Paulo, covering the same area of our collected data. These automatic stations measure CO and other pollutants in the streets. Here, these data were used to test whether possible reductions in CO could be inﬂuenced by other conditions, like meteorological elements. Statistical analysis Descriptive statistics were calculated for CO level in both the pre-ban and post-ban periods across the whole dataset and then subdivided by location within the venue and venue type. Data are presented as means6SE. Pearson’s correlation coefﬁ- cients were used to explore correlations between different environments of a particular venue. Differences in the pre-ban measurements according to venue type and measurement location were analysed by one-way and two-way analysis of variance. Differences between pre-ban and post-ban concentrations were analysed by one-way and two- way analysis of variance for repeated measures. Differences in expired CO concentrations in venue employees were analysed by a two-way analysis of variance for repeated measures (using time and smoking status as strata). Probability values of #0.05 were considered statistically signiﬁcant. Statistical analysis was carried out using SPSS V.13.0. 157