Hepatitis B virus infection in a population exposed to occupational hazards : firefighters of a metropolitan region in central Brazil

Introduction: By the nature of their activities, firefighters are exposed to a high risk of contracting hepatitis B virus (HBV) as most of the Fire Brigade occurrences in Campo Grande, State of Mato Grosso do Sul (MS), Brazil, are related to the rescue of victims of traffic accidents and the transportation of clinical and psychiatric emergencies. The aim of this study was to investigate the seroepidemiological profile of HBV infection in firefighters from the City of Campo Grande, central Brazil. Methods: The research involved 308 firefighters. After giving written consent, they were interviewed and blood was collected for the detection of HBsAg, anti-HBs and total anti-HBc of enzyme-linked immunosorbent assays (ELISA). Results: The participants had an average of 36.4 years of age (SD ± 6.5), being 89.9% male. Blood tests revealed 6.5% of seropositivity for hepatitis B (HB) infection (n=20), and 1% for HbsAg. Isolated anti-HBs markers, indicative of vaccine immunity, were found in 66.9% of the participants and 28.2% were susceptible to infection. With regard to risk factors for HB infection, multivariate regression analysis showed a statistically significant association with length of service; and prevalence was higher in individuals with over 20 years of service. Conclusions: The prevalence of HB found among the firefighters was low and length of time in the profession was found to be a risk factor. Non-occupational risk factors did not influence the occurrence of HB infection in the population studied.

Hepatitis B virus (HBV) infection is global in scope -about 600,000 deaths related to hepatitis B occur in the world every year 1 .Transmission involves contamination by blood and secretions and therefore these professionals, who are in permanent contact with this risk factor 2 , are directly exposed to it.
The risk of acquiring hepatitis B after being exposed to HBV-contaminated material from the source patient, with high viral replication rates, ranges from 22 to 31% and the risk of evidence of serological infection from 37 to 62%.In cases where the source patient has a low rate of viral replication, the risk of contracting HBV ranges from 1 to 6% and, in cases of seroconversion, from 23 to 37% 2 .In addition, the virus can remain stable for up to seven days at room temperature and in dry blood 3 .
Studies carried out involving different categories of healthcare professionals indicate that the prevalence of HBV infection has been found to be higher in nurses, primary care professionals, dentists and professionals working in laboratories and in services of hemodialysis, when compared with the general population (blood donors) [4][5][6][7][8] .
As firefighters act directly on pre-hospital care, they are apt to a high risk of getting infected by HBV because of the large amount of blood and body fluids with which they come into contact when rescuing victims of traffic accidents, medical emergencies and psychiatric disorders.The contact may occur with intact and broken skin, and with mucous membrane splashes during the rescue of people trapped in car wreckage, cuts from blood-contaminated broken glass and after rescue activities during the disinfection of materials and vehicles.
Research conducted in central Brazil with firefighters belonging to the rescue team who work in pre-hospital care reported a lack of preparation for self-protection, and low adherence to vaccination against hepatitis B 9 .Despite the urgency, national studies have not been conducted to estimate the prevalence of HBV infection in firefighters.Hepatitis B is a disease that can be prevented in the workplace through effective vaccination which is available and free of charge for professionals in situations of occupational hazard.The aim of this paper is to investigate the seroepidemiological profile and possible factors associated with HBV infection in firefighters who provide pre-hospital care in a metropolitan region of central Brazil.

Contrera-Moreno L et al -Hepatitis B virus infection in firefighters
All the firefighters of the Metropolitan Command Fire Department in Campo Grande, State of Mato Grosso do Sul (MS), Brazil, who provide pre-hospital care and face the risk of biological contamination in the carrying out of their activities, were invited to participate.The firefighters not involved in operational services were excluded.
Of the total number of firefighters (n=325), 308 professionals participated in the survey (94.7%).Six individuals refused to participate in the study, and eleven were not available during the survey period as they were on vacation, absent for health reasons, maternity leave etc. Data collection took place from January to December 2010 after the signing of the consent form.
A structured interview was conducted, using the outline prepared by the author, followed by blood collection (a previous pilot study had been carried out to adjust the instrument).In the corporation facilities after the interviews, blood samples were taken by venipuncture using vacuttainers.Serological tests were carried out at the Laboratory of Clinical Immunology, in the Department of Pharmacy-Biochemistry, Federal University of Mato Grosso do Sul (UFMS).
For the diagnosis of hepatitis B, all samples were initially tested for the detection of hepatitis B surface antigen (HBsAg), antibody to hepatitis B core antigen (anti-HBc), antibody to hepatitis B surface antigen (anti-HBs) by enzyme linked immunosorbent assay (ELISA) using commercial kits.HBsAg reagent samples were tested for the detection of hepatitis B e antigen (HBeAg) and antibody to hepatitis The average age of the participants was (n=308) 36.4 years of age (SD ± 6.5); 89.9% male and 11.1% female.As to education, 75.2% had attended school for 11 years and 21.5% were university graduates.90.9% belonged to lower military ranks (privates, corporals and sergeants) and 9.1% to the higher ranks (lieutenants, captains, majors, lieutenant-colonels and colonels).
Anti-HBs serology tests revealed that the immunization rate (85%) was higher in firefighters who reported three doses of hepatitis B vaccine (p <0.001 -chi-square trend test) than in those reporting one or two doses (62%, prevalence ratio (PR) 1.37, 1.16 to 1.61 95%CI) or those who did not receive the vaccine or who were unable to give information (19%, PR 1.87, 1.31 to 2.56 95%CI).
Regarding gender, there was no statistically significant difference in the prevalence of hepatitis B (p>0.05).The prevalence of the disease was approximately six times higher in the following cases: individuals over 45 years of age in relation to those under 25; those with less education (Table 1) in relation to those with university degrees; obese participants in relation to those with a normal body mass index (Table 2).
Of the 308 interviewees 51.6% reported having been immunized with three doses of the vaccine; 35.1% with one or two doses and 13.3% had no information or were not vaccinated at all.
No association has been seen between the prevalence of hepatitis B and the following variables: smoking, drinking, use of tattoos, B e antigen (anti-HBe).The test results were personally returned at a secret location, and the HbsAg-positive cases referred to the Center for Infectious Diseases of the University Hospital (NHU), UFMS.
Analysis of the data: the positive identification of HBsAg and/or anti-HBc markers was considered as a dependent variable; the independent variables were demographic data and behavioral and labor risk factors.In order to investigate possible associations between variables, chi-square, chisquare trend test and Fisher exact tests were used and prevalence ratios were calculated, with respective confidence intervals of 95%.To estimate the adjusted prevalence ratios, Cox regression was used (with time equal to one unit).
In constructing the multivariate model, variables with statistical significance lower than 20% have been selected, and then the backwardselection was performed.As relevant misleading events were not detected with the exclusion of variables, one by one, there remained the pre-selected statistically significant variables.Computer programs BioEstat version 5 and Epi Info 3.5.3 10,11were also used.

Ethical considerations
The project was approved by the UFMS Ethics Committee on Human Research and is registered under Protocol 1361 -26 th March, 2009.immunization against hepatitis B, number of sexual partners, condom use or sexually transmitted diseases, according to results of Table 2. Table 3 presents the risk factors associated with occupational exposure.It was observed that the prevalence of hepatitis B increases with length of service: it is higher in firefighters with more than 20 years of service (prevalence 19.6%), followed by 4.2% in individuals with 11 to 20 years of service; and 3.3% in subjects with under 10 years of service (p<0.001).The variables in question such as: rank, predominant type of function, overtime and another paid activity were not associated with a higher prevalence of hepatitis B infection.
Work-related accident cases had been attended to by 64% of the interviewees (197/308) and of these 74% (146/197) had been the intact-skin contact type.
No association was seen between the occurrence of HBV infection and the following variables: use of incomplete personal protective equipment (PPE) or the occurrence of occupational accidents with biological material (quantity and type), as shown in Table 3.
Multivariate regression analysis indicated that age, educational level and BMI were no longer associated with the prevalence of HBV infection; the association remained only in relation to the length of service (Table 4).This is the first study of seroprevalence of HBV infection in firefighters in Brazil.The overall prevalence of infection was 6.5% higher in comparison to studies involving healthy military personnel in Peru (0.58%) 12 and firefighters in England (0.42% in Gloucestershire 13 and 0.6% in Yorkshire 14 ), this being similar to a study of American firefighters (7.8%) 15 .

DISCUSSION
When compared to research involving other professionals exposed to the risk of occupational HBV infection, the overall prevalence of infection found in this study was similar to that of anesthetists (8.9%) 16 and lower than that of dentists (10,8%) 6 , laboratory workers (24.1%) 8 and primary care professionals (11.1%) 5 .In comparison to a recent study of Brazilian blood donors, firefighters had a similar infection rate: donors in Central Brazil presented a prevalence of HBV infection of 5.3% 17 .
Regarding positivity for HbsAg, findings show a higher rate (1%) in comparison to studies conducted in the same region of the country involving pregnant women (0.3%) 18 and prisoners (0.5%) 19 .

Behavioral risk factors
No statistically significant association was found between the factors associated with sexual behavior and hepatitis B infection, possibly because these issues are more difficult to approach.These findings diverge from those of another study conducted with a similar population, in which Averhoff et al. 20 , analyzing public safety professionals, including firefighters, found non-occupational factors related to HBV infection, including a history of sexually transmited diseases (STDs).

Occupational risk factors
The length of service of firefighters was a statistically significant association.The occurrence of HBV infection was directly proportional to length of service, being more common in individuals with over 20 years of service.Studies carried out with Brazilian healthcare workers in hospitals 21 , dentists 22 and hemodialysis workers 23 also revealed an association with length of service.Such data reinforce the possibility of occupational infection, as the awareness of occupational hazards was scarce 20 years ago and the use of PPE was not part of the practice of firefighters.They reported that the activities used to be done without gloves, masks or goggles.
Research conducted with American firefighters found that the contact of blood with intact skin may increase the risk of HBV infection 15 .In the present study, 74% of the firefighters who had suffered work-related accidents, reported intact-skin contact.Studies with healthcare professionals have shown that cases of occupational transmission by sharp materials represent a minority of cases and that many do not know how exposure occurred 23 .It is also worth mentioning that contamination may be indirect, through surfaces, since the virus survives for up to one week out of the human body 2 .This finding needs further investigation into the circumstances under which these accidents occur in intact skin.In this study interviews revealed that a large number of accidents involved exposure to a huge amount of blood on the skin, and that many cases are not reported because they think that the exposure poses no risk and is part of the job.Accidents involving mucous membranes, non-intact skin and perforations pose a higher significant risk of infection, and thus require greater attention on the part of the firefighters, who immediately seek healthcare services.It is known that, in the event of an accident at work, besides the vaccine, there is the hyperimmune immunoglobulin, also recommended as a means of preventing infection in those who are not immunized 2 .

Immunization against the hepatitis B
According to reports from the firefighters, only 51.6% had three doses of vaccine against hepatitis B. This immunization rate is considered low, since the firefighters are considered professionals facing a high risk of occupational infection and, on account of this, included in the National Calendar of Immunization 24 .In a study carried out with American firefighters in 2004, the rate of vaccination with three doses was 63.3% 25 , that is, higher than that found in this study.
The results of the anti-HBs marker indicated that 66.9% had vaccination immunity and, added to those who acquired immunity from the infection, 71.8% were HBV-immune.These data are similar to those found with other healthcare professionals in Brazil, like primary-care workers (75.3%) 5 and anesthesiologists (72.2%) 16 .
Nevertheless, it should be noted that 28.2% remain susceptible to infection.This is still a high number though, considering that many firefighters present incomplete (35.1%) or no immunization (13.3%).To reach complete immunity to HBV infection three doses of vaccine are required.After the three doses the anti-HBs testing is needed to confirm immunity.After a sequence of six doses the individual is considered non-responsive 26 .
In this study 85% (p<0.001) of individuals who reported three doses of vaccine were immune to hepatitis B. These data are compliant with the findings of another study involving professionals in the department of public safety, including firefighters 27 .In a recent study the efficacy (98.6%) of the Brazilian hepatitis B vaccine was proven when administered at recommended intervals: zero, one and six months after the first dose 28 .In this study, however, when there was no vaccination card, the reports of the interviewees have been considered, which may fail to be trustworthy as some of them may be confused as to the vaccines taken and the number of doses administered.In addition, in some cases, long intervals between one dose and another have also been observed.Immunization against hepatitis B is an effective weapon for preventing the spread of the disease, which has been proven by research years after the introduction of the vaccine 25,29 .This study has shown the need for actions to avoid infectious diseases in the workplace, especially hepatitis B as it is easily transmitted.Moreover, professionals can count on a national immunization program.The vaccination of all these professionals should be carried out in the workplace so as to facilitate overall adherence, preferably at the beginning of their work activities, that is, during the initial training course.

TABLE 2 -Distribution of firefighters according to risk factors associated with hepatitis B virus infection in Campo Grande, State of Mato Grosso do Sul, Brazil, 2010 (n=308).
Note: Statistically significant difference if p<0.05.The category not informed, if present, was suppressed of the test calculation.Anti-HBc: antibody to hepatitis B core antigen; 95%CI: 95% confidence interval; BMI: body mass index.HB: hepatitis B; STD: sexually transmitted diseases; a Fisher exact test; b Chi-square test; c Chi-square trend test.

TABLE 3 -Distribution of firefighters according to factors associated with occupational exposure and hepatitis B virus infection in Campo Grande, State of Mato Grosso do Sul, Brasil
-Note: statistically significant difference when p<0.05.The category Not informed, if present, was suppressed of the test calculation.Anti-HBc: antibody to hepatitis B core antigen; 95%CI: 95% confidence interval; PPE: personal protective equipment; WRA: work-related accidents.a Chi-square test; b Chi-square trend test; c Fisher exact test.