Annual Risk Of Tuberculous Infection Research Articles

Comparison of effectiveness of BCG vaccination and preventive therapy in Japanese settings, with special emphasis on the sensitivity and specificity of tuberculin testing

BCG vaccination in low prevalence countries is controversial. Most discussions have been done by the comparison of benefit, side effect and cost of BCG vaccination. No discussion has been done on the disadvantage of BCG vaccination from the point of view of loss of sensitivity and specificity of tuberculin test on the diagnosis of LTBI. Three groups, i.e. the BCG vaccination group with preventive therapy under worsened sensitivity and specificity of tuberculin test due to previous BCG, no intervention group and non BCG vaccination group with preventive therapy under standard sensitivity and specificity of tuberculin test were set up. The target population was a cohort of Japanese who are born at the year with 0.1% annual risk of tuberculous infection. The TB incidence, TB related mortality (including death by BCG and preventive therapy), TB related loss of DALY (disability adjusted life years), and direct medical cost of the above three groups, for the cohort only and the cohort including secondary TB cases from the clinical cases in the cohort. Under the current program conditions, the merit of BCG vaccination is greater than the merit obtained from the preventive therapy without BCG. Although the medical direct cost is lowest among the preventive therapy group without BCG, next without BCG or preventive therapy and highest among BCG group. Under BCG group, too extensive screening for LTBI does not reduce the loss of TB related DALY, whereas in the non BCG group, extensive screening will help to reduce the loss of TB related DALY and if more extensive screening can be done, the loss of TB related DALY in the non BCG group can be less than that in the BCG group. At present extensiveness of screening for LTBI and BCG vaccination contribute to the reduction of TB and loss of TB related DALY. Possible extensive screening without BCG may be able to reduce loss of TB related DALY in comparison to the BCG vaccination group.

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

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. 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. 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. 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.

Estimation of the annual risk of tuberculosis infection for white men in the United States.

The annual risk of tuberculous infection for white men in the United States was estimated from published tuberculin surveys and found to be related to tuberculosis incidence as reflected in the annual case rate during the past 3 decades, with a constant ratio of approximately 150. It is currently estimated to be 0.03%/year. The technique developed for this estimation is not complex and should be applicable to other segments of the population for which suitable data are available.

Use of two methods of analysis to estimate the annual rate of tuberculosis infection in Southern Algeria

Setting: Analysis of tuberculin skin test surveys. Objective: To estimate the annual tuberculous infection rate in Tamanrasset (southern Algeria) by applying on the one hand the classical method of the Tuberculosis Surveillance Research Unit (TSRU) of the International Union Against Tuberculosis, and on the other the study of variations of allergy published by Raj Narain et al. Methods: 3675 pupils aged 5–18 years were tested in October 1982 or November 1983; 1240 of them were tested on both occasions. The technique of the World Health Organization, with 2 TU PPD RT23 tuberculin was used by trained testers. The TSRU method was applied to the 863 children aged 5–15 years without bacille Calmette-Guerin (BCG) scar, according to three estimates of the prevalence of infection (cut-off points of the distribution of reactions of 10 mm, of 14 mm corrected by dividing by 0.82, and mirror technique with a mode of 17 mm), and to three hypotheses of the decrease in infection risk (1%, 3% and 5%). The study of variations of allergy was used in the 1240 pupils tested twice (BCG-vaccinated or not). Results: The average annual risk of tuberculous infection estimated by the TSRU method was lower than 1 % (0.5%–0.6% according to the most stringent criteria). By the method of variations of allergy, the estimated annual infection rate was 0.9%. For the latter, our results are consistent with those obtained by other researchers. Conclusions: These findings suggest that the study of variations of allergy might be a good alternative approach to estimate the annual infection rate in countries where children are BCG-vaccinated at birth, which is the case for most developing countries.

193-PA10 National tuberculin survey of Kenya 1986–1990. Results and trend of the annual risk of tuberculous infection from 1959 till 1989

193-PA10 National tuberculin survey of Kenya 1986–1990. Results and trend of the annual risk of tuberculous infection from 1959 till 1989

Trend in tuberculous meningitis in Barcelona in children aged 0–4 years: correlation with the annual risk of tuberculous infection

Setting: All the paediatric hospitals in the province of Barcelona. Objective: To examine the trend in the incidence of tuberculous meningitis (TM) in children aged 0–4 years and its correlation with the annual risk of tuberculous infection. Design: Survey conducted between 1975 and 1991. Results: 157 cases of TM in children aged 0–4 years were diagnosed between 1975 and 1991. A constant decrease during the prospective period is observed from 21 cases of TM in 1977 to only 2 cases in 1991 with an annual decrease of 5.5%, which is smaller than the 8% annual decrease of the annual risk of tuberculous infection. A close correlation between the observed incidence of TM and the average annual risk of infection to which children in the same area were exposed r = 0.9156 ( P < 0.0001) is verified. Moreover, this correlation gets even closer when considering the annual risk of infection as a percentage of the TM incidence, since a stable correlation of about 1% (0.89–1.39%) is demonstrated. Nevertheless, the incidence and the number of observed cases of TM is twice that expected if one refers to the Table that calculates meningitis cases by means of the annual risk of infection. We observed one case of TM among 218–384 infected children, i.e. a risk of developing TM of 0.19–0.26%, higher than that found in the countries with the most favourable tuberculosis situations. The sharp decrease of TM coincides with the suppression of BCG-vaccination in Barcelona, which suggests that it has not substantially changed the decrease of the risk of developing TM in children under 5 years of age. The decrease in the annual risk of infection, and consequently TM, is essentially due to the improvement of treatment in adults. Conclusion: It is confirmed that the incidence of TM in children under 5 years represents 1% of the annual risk of infection. The TM incidence thus permits the determination of the annual risk of infection when the conditions to calculate it directly do not exist.

Six years' experience with the discontinuation of BCG vaccination: 2. Cost and benefit of mass BCG vaccination

In 1986 the compulsory mass BCG vaccination of infants born in a selected area of the Czech Republic was abolished. The observed annual risk of tuberculous infection in children aged 0–6 years was below 0.1 % and the annual risk of tuberculous disease 7/100 000. The increase of tuberculous cases among nonvaccinated children indicated a protective efficacy of BCG vaccine of 80%. A benefit analysis proved that the advantages and disadvantages of BCG vaccination were in balance. The number of nonvaccinated children developing tuberculosis was so small that mass application of BCG has been found to be redundant. The important advantage of not using the vaccination is the maintenance of the epidemiological and diagnostic value of tuberculin tests. The tests in connection with preventive chemotherapy remain an important tool, enabling control of infected individuals.

The supply of antituberculosis drugs and national drugs policies

The money necessary for purchasing antituberculosis drugs in a national programme comes from the Public Health Services budget, funds from the health insurance scheme (when it exists) and household budgets. The Public Health Services budget is on average $2–23 US per year and per person in low or middle income countries. Average drug consumption in these groups of countries was from $2–26 US per person in 1990. The number of patients to be treated depends on the annual risk of tuberculous infection (ARTI) and the case detection rate: it is the same when the ARTI is 1% and the detection rate 100%, and when the ARTI is 2% and the detection rate 50% of cases. The supply of antituberculosis drugs has a real cost representing around 3% of global drug consumption in low income countries and is always less than 1% of global drug consumption in middle income countries. In most developing countries it could be covered with the aid of national financial resources, on condition that it is integrated into a coherent national drugs policy aimed at guaranteeing the continued availability of essential drugs.

Epidemiology of tuberculosis in the United States.

Over the past 30 years, the risk of tuberculous infection is estimated to have declined by approximately 8.3 per cent annually. Over that period, the incidence of tuberculosis declined between 5 and 6 per cent annually, and the mortality rate has declined by about 7.3 per cent annually. However, tuberculosis has not receded uniformly among all segments of the population. The steepest decline has been observed in children five to 14 years of age, and the smallest decline has been observed in the elderly. Among adults, the decline has been steeper among whites than among other racial groups. In the 1980s, the annual risk of tuberculous infection in the general population is estimated to be as low as or lower than one in 10,000. It is narrowly concentrated among contacts, particularly close contacts, of known cases. The risk is highest among those who are exposed to sputum smearpositive cases. The incidence of tuberculosis in 1987 was 9.3 per 100,000 in the general population, but varied widely among different segments of the population. Although incidence increases with age among all race and ethnic groups, cases in minorities are concentrated among young adults, while cases in non-Hispanic whites are concentrated among the elderly. These differences are mostly attributable to differences in the risk of tuberculous infection, because, once a person is infected, the risk of progression to tuberculosis is similar among blacks and whites and among males and females (although two age groups, young children and adolescents, appear to be especially prone to progression). This suggests that with the passage of time, succession of new generations experiencing lower risk of infection will reduced the prevalence of tuberculous infection much more rapidly in the non-Hispanic white population than in minority populations. Among factors that modify the risk of progression from subclinical infection to tuberculosis are recency of infection and infection resulting from transmission by a sputum smear-positive source case. Only a few of the many risk factors that have been identified as promoting progression can be considered major contributors to morbidity, because most are not highly prevalent. A major exception may be HIV infection, which, although not yet highly prevalent in the US population, appears to be the strongest factor yet identified that is capable of promoting progression to tuberculosis.(ABSTRACT TRUNCATED AT 250 WORDS)