Risk of infection with Mycobacterium tuberculosis in Malawi: national tuberculin survey 1994.

OBJECTIVE: To estimate the annual risk of tuberculosis infection among schoolchildren in Malawi. METHODS: A school survey was conducted in twelve randomly selected districts in Malawi. Children in standard 1-4 and aged 6-11 years were eligible. Tuberculin skin testing was performed according to World Health Organization/International Union Against Tuberculosis and Lung Disease guidelines. RESULTS: Of the 17123 eligible children, 80% were tested. Of those tested 79% were read. The prevalence of infection according to various criteria was 9-12% in children without bacille Calmette-Guerin (BCG) scar. The prevalence of reactions of 10 mm or more was lower in girls than in boys, increased with age, and was higher in those with than in those without BCG scar. The annual risk of infection was estimated to be within the range 0.6-1.4%. CONCLUSION: Annual risk of infection in Malawi was in the order of 1%. This study is expected to provide valuable baseline information for an assessment of the impact of human immunodeficiency virus (HIV) on tuberculosis transmission in Malawi.

Tuberculosis and the HIV epidemic: increasing annual risk of tuberculous infection in Kenya, 1986-1996.

OBJECTIVES: The purpose of this study was to assess the impact of the increased incidence of tuberculosis (TB) due to HIV infection on the risk of TB infection in schoolchildren. METHODS: Tuberculin surveys were carried out in randomly selected primary schools in 12 districts in Kenya during 1986 through 1990 and 1994 through 1996. Districts were grouped according to the year in which TB notification rates started to increase. HIV prevalence in TB patients and changes in TB infection prevalence were compared between districts. RESULTS: Tuberculous infection prevalence rates increased strongly in districts where TB notification rates had increased before 1994 (odds ratio = 3.1, 95% confidence interval = 2.3, 4.1) but did not increase in districts where notification rates had increased more recently or not at all. HIV prevalence rates in TB patients were 50% in districts with an early increase in notification rates and 28% in the other study districts. CONCLUSIONS: Countries with an increasing prevalence of HIV infection will need additional resources for TB control, not only for current patients but also for the patients in additional cases arising from the increased risk of TB infection.

National tuberculin survey of Kenya, 1986-1990.

SETTING: The first tuberculin survey conducted in Kenya by the World Health Organisation in 1958-1959 found an annual risk of tuberculosis infection (ARTI) of 2.5%. OBJECTIVE: To estimate the ARTI and its trend in recent years and to compare the estimated incidence rates with the notification rates. DESIGN: A tuberculin survey was held in 12 randomly selected districts in the period 1986-1990. Tuberculin testing with 2TU PPD RT 23 + Tween 80 was performed in 40,365 primary schoolchildren aged 6-13. RESULTS: Of 14,984 non BCG-vaccinated children, 1,380 (9.2%) had indurations of > or = 10 mm. Double testing with PPD RT 23 and PPD-scrofulaceum in 980 non BCG-vaccinated children revealed a high level of infections due to mycobacteria other than tuberculosis (MOTT). Therefore, the prevalence of tuberculous infection was based on the sum of 50% of the indurations of 17 mm and all indurations of 18 mm or more multiplied by two. The prevalence of tuberculous infection in schoolchildren aged on average 8.4 years, 'weighted' for the population size according to the provisional results of the 1989 census, was calculated at 5.5%. The corresponding ARTI is 0.6%. CONCLUSION: The ARTI has declined by an average 4.6% per year. The tuberculosis problem differs from one area to the next, with the highest prevalences of infection on the coast and in Eastern Kenya, and the lowest in Western Kenya. Although the average ratio of observed and estimated incidences indicate that 70% of incident cases are notified, considerable inter-district variations are observed.

Sensitivity to PPD tuberculin and M. scrofulaceum sensitin in schoolchildren BCG vaccinated at birth.

OBJECTIVE: To determine the degree of and variation in sensitivity to PPD RT 23 tuberculin and M. scrofulaceum sensitin RS 95 at school age in children BCG vaccinated at birth. DESIGN: Double-testing by applying standard WHO Mantoux tests and inspecting BCG scars. SETTING AND PARTICIPANTS: Urban and rural schools in Southwest Finland, 1091 children aged 11-13 years. MAIN OUTCOME MEASURES: Size of tuberculin and sensitin indurations and BCG scar (mm). RESULTS: The mean size of tuberculin indurations was 7.2 mm, sensitin indurations 8.1 mm and BCG scars 7.9 mm. The reaction to sensitin was significantly larger than to tuberculin (95% confidence interval 0.58-1.10 mm) and the zero reactions to sensitin were fewer. Correlation between tuberculin and sensitin indurations was significant (r = 0.75, 95% confidence interval 0.72-0.77). There were induration greater than or equal to 15 mm to tuberculin in 16% and to sensitin in 14%. Sensitin indurations exceeded those of tuberculin by 4 mm or more in 14% of the children with at least 5 mm tuberculin indurations. CONCLUSIONS: High tuberculin sensitivity in healthy schoolchildren may be partially maintained by contact with environmental mycobacteria. Our data do not prove but very probably indicate that children have protective immunity. In view of the current incidence of tuberculosis in Finland and the likelihood that lymph node infections and sensitivity to environmental mycobacteria will increase, continued BCG vaccination at birth is recommended.

Report of a study into skin sensitivity and into scar diameter after vaccination with BCG in 5,000 new-borns in Cakovec, Yugoslavia.

To compare the skin allergy producing potency of batches of BCG from three different production centers, 5,066 new-borns were vaccinated with one of there batches (one from the Netherlands, one from Yugoslavia and one from Denmark). Six, twelve and twenty-one months after vaccination tuberculin testing was done and the diameter of scars was measured in subgroups. Skin allergy through BCG-vaccination was registered to be highest after 6 months and appeared to wane rapidly afterwards. There was a definite difference in the skin allergy potency between the three vaccines. The difference in scar diameter was less pronounced. In 5,066 vaccinated new-borns 137 (2.7%) enlarged axillar glands were registered. There appeared to be a positive correlation between the mean Mx-induration 6 months after vaccination and the percentage of enlarged glands. No serious complications have been registered so far.

Multiple skin testing of Kenyan schoolchildren with a series of new tuberculins.

This study on Kenyan schoolchildren aims to elucidate the effect of contact with environmental mycobacteria on the development of specific delayed hypersensitivity. A series of 12 skin test reagents was employed; eleven of them were prepared from extracts of living mycobacteria and the last was the P.P.D. RT 23. Eight of the new tuberculins were prepared from mycobacteria recovered from the East African environment. A total of 8641 tests were carried out on 4320 children between the ages of 6 and 17 years in four townships. Two of these townships were in fertile agricultural areas and two were in the desert. Just over 80% of the children had received BCG immunization The results obtained showed that increasing age, geographical locality and BCG immunization all had a profound effect, and socioeconomic background had some effect, on the pattern of reactivity to the various reagents. The rationale behind the use of the series of new tuberculins and the results obtained with them are discussed in relation to the interacting effects of the factors complicating these results.