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Brief Reports Indian Pediatrics 2002; 39:362-365 |
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Prevalence of Tuberculous Infection and the Impact of BCG Vaccination on Tuberculin Testing Among Primary Schoolchildren in Turkey |
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Tuberculosis is still a major health problem throughout the world, especially in developing countries(1,2). The use of Bacillus Calmette-Guerin (BCG) vaccine has been limited because its effectiveness in preventing infection and infectious forms of tuberculosis is uncertain and the reactivity to tuberculin that occurs after vaccination interferes with the management of persons who are possibly infected with M. tuberculosis. However, it plays an important role in preventing life-threatening forms of tuberculosis in infants and young children(3-6). Therefore, World Health Organization (WHO) recommends BCG vaccination as a public health measure in developing countries with a higher prevalence of tubercular infection (1% , and upper)(6,7). The tuberculin skin test, which is based on the detection of delayed hypersensitivity to the antigens of M. tuberculosis, is used as a parameter for the determination of infected children. Purified protein derivative (PPD) is the preferred skin test antigen and is used for the intradermal Mantoux test. Previous vaccination with BCG can cause a reaction to tuberculin skin test and so alters tuberculin response(1,8). In this study, we aimed to deter-mine the impact of BCG vaccine on tuberculin test about 6-9 years after vaccination and prevalence of tuberculous infection among primary schoolchildren in Sanliurfa, a south-east Anatolia region of Turkey. Subjects and Methods The study was carried out on 1398 healthy children among 6-9 years old, presumed BCG vaccinated subjects at birth or in first few months of life. These were selected by group sampling method from ten different primary schools in Sanliurfa during March-May 1998 period. Children who had abnormal conditions which may affect PPD response such as co-incident clinical viral infections, immunization with an attenuated virus vaccine, treatment with immunosuppressive agents, severe mal-nutrition, neoplastic diseases and other chronic systemic diseases were not included in the study. Two pediatricians performed all pro-cedures. Children were regarded as BCG-vaccinated on the basis of presence of scar on left shoulder. Tuberculin skin test with 5 tuberculin units of PPD antigen (RT Tween 80) was administered to children by intra-dermal Mantoux method and the site of antigen injection was examined for occurrence of induration after 48-72 hours. When indurated PPD reactions were 10 mm and more in unvaccinated children and 15 mm and more in vaccinated children, the test results were defined as "positive"(9-11). Children with positive test were regarded as infected with M. tuberculosis and were referred to the local tuberculosis control center wherein further exmainaltion and investigations were conducted(10). The prevalence of tuberculosis infection (PTI) was evaluated with following formula(12): the number of children with PPD ³ 10 mm and no BCG and number of BCG scar positive children with PPD ³ 15 mm as a percentage of total population screened. Statistical analyses were performed by Chi-square test using SPSS for Windows program. Results While 688 (49.2%) children had no BCG scar (unvaccinated), 710 (50.8%) children had one scar (vaccinated). Tuberculin positivity rates representing infection with M. tuber-culosis in unvaccinated (6.5%) were higher (p >0.05) than that of vaccinated children (4.5%) (Table I). Tuberculin negativity rates in vaccinated children (85.6%) were lower (p >0.05) than that of unvaccinated children (93.5%). The prevalence of tuberculosis infection (PTI) was 5.5%. No active tuber-culosis was found in tuberculin-positive cases.
Discussion BCG is the only commercially available vaccine against tuberculosis and is commonly used in many developing countries to prevent tuberculosis for a long time(1,7,13,14). The official recommendation of the WHO is a single dose administered during infancy, but recommended vaccine schedules vary widely among countries(6,7,13). Because of the high prevalence of tuberculous infection in our country, BCG vaccination has been accepted as a part of national immunization program applied routinely by Health Ministry(12). According to this, Turkish children should be revaccinated as five-seven years old after the first BCG vaccination at two moths of age. While the average rate of unvaccinated children is 35% for Turkey, it was 49.2% in our study(12,15,16). This result shows that BCG vaccination according to age was insufficient and routine BCG vaccination of infants has been somewhat neglected in our country and also Sanliurfa region, nowadays. In general, a tuberculin skin reaction ³ 10 mm in a BCG-vaccinated child indicates infection with M. tuberculosis and necessitates further diagnostic evaluation. But, previous vaccination with BCG can cause a reaction to tuberculin skin test and so alters tuberculin response(1,8). Therefore, we utilized a cut off ³15 mm (95th percentile value determinated previous studies), in BCG-vaccinated children due to natural infection(11). BCG vaccination has had little effect on prevention of tuberculous infection. However, it plays an important role in prevention of life-threatening forms of tuberculosis in infants and young children(1,3-6). Several studies have reported that BCG vaccination and revaccination decrease the ratio of tuberculin negativity and yield a stronger immune response(11,16). Also, both tuberculin positivity rates representing infection with M. tuberculosis and tuberculin negativity rates in vaccinated children were lower than those of unvaccinated children in our study. But the difference between these groups was not statistically significant (p >0.05). Therefore, our findings may indicate that BCG vaccine has no protective effect against tuberculosis infection. The prevalence of tuberculosis infection is important fo the estimation of infected human pool in community. This criteria is especially important for an unvaccinated population(13,17). The prevalence of tuberculous infection has decreased from 56% in 1959 to 25% in 1982 and averaged 3.8% in 1990s in Turkey(12,15,16). Our finding for Sanliurfa region which is 5.5% is slightly higher than that of the mean value of Turkey and developed countries (<1%)(7,18). In conclusion, our study showed that the prevalence of tuberculous infection is high in Sanlliurfa region and VCG vaccination has no effect on prevention of tubercular infection. However, BCG vaccination may be effective in prevention of life-threatening forms of tuberculosis in infant and young children(1,3-6). Therefore, we suggest that BCG vaccine should be administrated more effectively as a method of prevention of tuberculosis on a community basis in Turkey and similar countries in which the prevalence of tuber-culosis infection prevalence is high. Contributors: MK coordinated the study and drafted the paper (particularly its design and interpretation); he will act as guarantor for the paper. HHE and AA participated in the data collection. HHE, MMT and AK helped in drafting the paper. Funding: None. Competing interests: None stated.
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