Tuberculosis in the Asia Pacific Region

The tuberculosis situation in 46 countries in Asia is reported. TB is still prevalent in Asia and more than 5 million or 60% of new TB patients in the world occur in Asia annually. Prevalence of TB is high in rural and urban areas, the young and the aged, female as well as males. Because of high prevalence of TB and delay in case-finding, annual risk of TB infection is still 1.5% or more in almost all countries. The cure rate by standard chemotherapy is often less than 50%, so that the prevalence of initial drug resistance is very high in many countries. As a result, TB is not decreasing to a satisfactory degree in almost all the developing countries of Asia. To improve this situation, WHO Headquarters presented a new TB control strategy recently. Priority is given to curing 85% of detected smear positive cases in all the developing countries by the introduction of short-course chemotherapy including rifampicin, and to detecting 65% of existing smear positive cases. The author stresses the importance of improvement and activation of the TB control program in Asian countries for TB control in the world.

At the World Health Assembly held in May 1991, a resolution to strengthen the tuberculosis (TB) control programme was adopted.The National Tuberculosis Control Programme (NTP) was established more than 20 years ago in almost all the countries of the world, and has since been carried out actively.However, the achievements were, not so satisfactory in many developing countries, where TB problems remain unchanged, or have become bigger and more complicated, though many people or even many doctors still think that "TB is a disease of the past".
As TB in Asia is so important at present from the point of view of TB control strategy in the world, and the situation is not so clear for the doctors in the Asia Pacific area, this paper is focused on "TB in Asia Pacific Region" instead of "TB in the Asia", more exactly, focused on 46 countries in the South East Asia Region and the Western Pacific Region by the WHO's classification of the regions, covering 58.4% of the world's population, or 3,000 million out of 5,200 million.
It is difficult to estimate the magnitude of the TB problem from.official statistics because only six of the 46 countries reported TB mortality in 1988.Even the number of TB deaths is far from clear.Therefore, one has to estimate the TB situation from the annual risk of TB infection (ARI), calculated from the results of tuberculin surveys carried out in each country.It was confirmed repeatedly that 1% of ARI corresponds to the incidence of 50 smear positive cases per 100,000 from the results of analysis of the data in pre-chemotherapy era in European countries, or the recent data comparing the results of TB prevalence surveys and ARI in many developing countries, so that it is possible to estimate the incidence of smear positive cases in these countries.
Thus, it is estimated that the total number of new cases of smear positive and negative TB (including extra-pulmonary TB) are 8 million in the world annually, as shown in Table 1.The ratio of smear positive cases to negative cases is almost 50 to 50.Both of the estimated number of new cases in the South East Asia Region and the Western Pacific Region are almost 2.5 millions.Each region has almost 30% of total TB patients in the world, which means that these two regions combined have more than 60% of TB patients in the world.The prevalence of TB is around double the incidence, so it is estimated that 16 million people are suffering from TB at present in the world.Of these, 26% or 4.2 million TB patients are living in China, 30% or 4.8 million in the Indian sub-continent, and 6% or 1 million in other parts of Asia.
One of the reasons why there are so many TB patients in the world is that more than 30% of the world's population, or 1,722 million have been already infected with TB bacilli.They can develop TB without new TB infection.It is estimated that 43.8% of the people in the Western Pacific Region have been already infected with TB bacilli as shown in Fig. 1.
In the industrialized countries, many of the aged but very few of children and only a minority of the young aged 20 to 39 years are infected with TB bacilli, while more than half of the young are already infected in the developing countries.And some of them can develop the disease without no recent infection.They often continue to discharge TB bacilli for such a long duration that many children and infants will be infected with TB bacilli from these patients, and many of them in turn will develop TB.For example, Fig. 2 shows the age specific prevalence of bacilli positive TB cases in the Philippines according to the results of a nationwide TB prevalence survey carried out in 1981-83.The prevalence of smear positive cases is 0.91% among young adults aged 20-29, and it is as high as 1.84% among people aged 30-39 years.
Prevalence of bacilli positive TB cases are high in males as well as in females.Fig. 3 shows According to the second TB prevalence survey in China carried out in 1984 and 1985, the prevalence of TB differ greatly from area to area.In Fujian Province, the prevalence of smear positive cases was 246 per 100,000, 4.6 times higher than that of the lowest province, Gansu Province, where it was 54 per 100,000.As shown in Fig. 4, TB is often prevalent in rural areas, while TB prevalence is rather low in capital cities and big cities.
Moreover, TB is not decreasing satisfactorily in the Western Pacific Region and South East Asian Region, according to the results of the survey undertaken by EPI.It seems that the registration rates are low and the size of the population increasing year by year, and as a result, the number of TB cases is increasing annually in many developing countries.
The main reason why TB does not decrease in many developing countries is that the cure rate of treatment is very poor.Table 3 shows the treatment results by standard regimen (chemotherapy without RFP) in several countries.The cure rate is 53.8% to 74.9%.These are the optimum cure rates by the standard regimen; the actual cure rate is less than 50% in many developing countries such as India, Bangladesh, and Nepal.
Failure cases by chemotherapy often discharge resistant bacilli.As a result, the prevalence of initial drug resistance to anti-TB drugs is becoming high in many Asian countries.Prevalence of drug resistance to rifampicin (R), isoniazid (H), streptomycin (S) and/or ethanobutol (E) in Korean has been fortunately decreasing recently, but it is still 16.5% as shown in Fig. 5.
TB mortality rates are still high in many Asian countries, too.It is estimated that the total number of TB deaths is about 3 million in the world even now, as shown in Table 4. Ninetynine percent of them occur in developing countries.Moreover, 80% of TB deaths in developing countries are observed in the economically most productive age groups of the population.It is estimated that TB accounts for 26% of all deaths in this age group.Fortunately, prevalence of HIV infection is still low in almost all the Asian countries.No increase of TB due to HIV infection is reported in Asian countries at present.
According to the WHO's estimation, the service coverage for the TB control is rather high in the Western Pacific Region, while it is not so high in the South East Asian Region as shown in Fig. 6.
After serious discussions, WHO Headquarter has set up new targets for its TB control program, as shown in Fig. 7.If the cure rate is lower, chronic bacilli dischargers will increase.As a result, the risk of infection will not decrease and the prevalence of initial drug resistance will increase.Therefore, even in low income countries with poor health infrastructures, we need to cure 85% of all detected cases.To achieve this goal, the introduction of short-course chemotherapy including refampicin (R) is essential, although it needs a large amount of budget.

Source:
WHO/TUB, 1990 Figure 6 Average and range of service coverage of tuberculosis control programmes, 1990 NA: Due to the lack of a method to estimate the incidence of tuberculosis when the annual rate of infection becomes low, it is impossible to monitor the case-finding coverage rate.At present, service coverage rates of NTP are less than 50% in many developing countries.
After getting an 85% cure rate, we need to detect 65% of existing smear positive cases.
There are many middle income countries in Asia, too.The targets of NTP in these countries are to cure 85% of the detected cases and to detect 85% of the smear positive cases.
Formerly, all TB doctors believed that TB could be controlled by a WHO policy such as passive case-finding by direct smear examination, ambulatory treatment by rather cheap chemotherapy regimens, integration of TB control activities into general health services, and so on.However, the results have not been so satisfactory.Nevertheless, many Asian doctors are forgetting about TB.It is strongly hoped that NTP will be implemented according to a new WHO policy and will become more active in all the Asian countries in the future.
Figure 4 Standardized smear positive prevalence by province and municipality in China, 1984/85

Figure 5
Figure 5 Trend of prevalence of resistance to anti-TB drug in Korea (Previously un-treated)

Figure 7
Figure 7 New tuberculosis control strategy targets and expected impact.

Table 1
Estimated Number of TB New-Cases in the world.1990 -A .Kochi -

Table 4
Estimated Number of TB Deaths by Region in the World (WHO, 1990)