The Topic of This Month Vol.27 No.10(No.320)

Tuberculosis as of 2005, Japan

(IASR 27: 255-256; October, 2006)

This topic deals with recent trends of tuberculosis (TB) incidence in Japan on the basis of the Annual Report on TB Surveillance in Japan 2005 summarizing the situation of registered TB cases (January 1-December 31, 2005) reported by prefectures, selected cities, and special wards through health centers.

Situation of newly registered TB cases: TB cases who have newly started TB treatment and were registered at health centers during 2005 counted at 28,319 (including foreigners), which are 1,417 fewer than those in 2004. The annual incidence rate of 2005 was 22.2 per 100,000 population, 5% decrease from 2004 (23.3) (Fig. 1). In 1999, TB emergency was declared by the government; however the incidence rate was on the continuous decrease for 6 years since 2000. The decrease has been slow, so that the current level of the incidence rate almost agrees to the extension of the slow declining trends seen during 1980's until 1996.

Clinical pictures of patients: The majorities (80%) of newly registered cases had pulmonary TB and the remainders extrapulmonary TB. Seventy-two percent of pulmonary TB cases were discharging tubercle bacilli, particularly 50% were sputum-smear positive, being especially important cases as sources of infection. The bacillary positive rate of pulmonary TB patients has continuously been on the increase for the past 30 years, reflecting the wider use of laboratory examinations of Mycobacterium tuberculosis , and bacteriological findings being receiving more and more stress rather than radiological findings. At the same time, it is also considered that cases being serious at the onset and those not diagnosed until becoming serious conditions are increasing. Under such circumstances, the incidence rate of sputum-smear-positive pulmonary TB does not show any decrease parallel to the incidence rate of TB of all forms (Fig. 1).

Of sputum-smear-positive pulmonary TB, recurrent (re-treatment) cases were seen in 7.6% of all ages. The corresponding proportion is 9.3% among those over 60 years of age, being higher than that for younger than 50s (4.7%).

The affected sites of extrapulmonary TB cases are the pleura in majority cases (77%), followed by the lymph node (peripheral, hilar), the vertebra, the bone, the joint, the intestines, and the urinary tract. Miliary TB as disseminated TB, classified as extrapulmonary TB, accounted for 10% of extrapulmonary TB.

Age of patients: The incidence increases almost uniformly with age over 5 years of age, reaching the highest level of 96.0 at the age over 80 years. Among young adults, increased risk of developing TB after infection is indicated; >20s (15.4), >30s (14.9), and >40s (14.0). The incidence of 20s in 2005 was slightly higher than that in 2004 (15.3).

As age-pattern of incidence, the proportion of cases aged over 60 years has been increasing among newly registered TB patients every year, and it exceeded for the first time 60% in 2005. If the age patterns of incidence are compared between 1975 and 2005 (Fig. 2: Note the different scales used for each year). In 2005, the pattern is becoming a Western countries' type as compared with that 30 years ago; conspicuous difference between aged persons over 70 years and those younger than 70 years is seen and a small peak is seen among 20s and 30s.

Incidence rate by geographical area: By prefecture, the incidence rate in Osaka (38.4) is the highest, followed by Tokyo (29.9), and Hyogo (27.4). Low incidence is seen in Nagano (10.7), Miyagi (12.0), and Yamagata (13.4). The geographical differences are still large (Fig. 3); particularly the incidence is high in such large cities as Osaka (58.8), Kobe (34.5), Nagoya (34.3), and Tokyo (33.9). Of these cities, incidence in Osaka City has been markedly improved; during four years from 2001, the incidence rate decreased by 29% (in other cities, the decreasing rates were less than 20%).

Mode of detection of cases: About 80% of cases visited a medical facility seeking care for their illness where they were diagnosed with TB. Besides, periodic check up detected 13%, and extraordinary examination, mainly contact investigation 3%. They were about the same as those in 2004. The proportion of those who were found by mass miniature radiophotography (MMR) (examination of workers and general inhabitants) was not so different from that in 2004 before the large change of the system by revision of the TB Prevention Law.

Among pulmonary TB cases, the patientfs delay from the appearance of respiratory symptoms to the first visit of medical facility for more than 2 months accounted for 18% and doctorfs delay from the initial medical consultation to establishment of TB diagnosis for more than a month accounted for 26%. These proportions have decreased slightly during the recent 5 years (in 2001, they accounted for 19 and 27%, respectively), showing improvement in delay in health action taking and indication of diagnosis.

Among 22,655 pulmonary TB cases, 54% were positive on smear examination, and the specimens for the smear examinations were sputum in 93% of them, bronchoalveolar lavage fluid 4%, and gastric juice 2%. Similarly, 43% were positive on culture, and the specimens were sputum (87%), bronchoalveolar lavage fluid (7%) and gastric juice (3%).

TB deaths: According to the Vital Statistics of Japan, death cases of TB during 2005 counted at 2,295 (35 less than the preceding year), annual mortality rate of TB being 1.8 per 100,000 population (Fig. 4), the cause of death by order ranked the 25th like that in the preceding year. This figure corresponds to about 8% of newly registered cases in 2005; in other words, about 8% of newly developed cases ultimately die of TB. On the other hand, 1,501 cancellations from registration due to TB death were reported and 1,340 of them were deaths of TB within one year after registration. This indicates that about 5% of newly registered cases died within one year after start of treatment.

Cases under registration and prevalence rates: TB registered cases as of the end of 2005 counted at 68,508, which were 3,571 less than that of the preceding year. The total cases with active pulmonary and extrapulmonary TB requiring treatment counted at 23,969, which was 2,976 less than that in the preceding year. The prevalence rate per 100,000 population was 18.8, and it decreased by 2.3 from 21.1, the figure of the preceding year (Fig. 5). The prevalence rate depends not only on the incidence rate but also on the duration of treatment and clinical outcome (death and defaulter from treatment). Particularly short-term chemotherapy has been widely accepted recently, curtailing the average duration of treatment to shorter than one year, and it has become clearer that the prevalence rate is lower than the incidence rate.

Results of treatment: Of primary treatment smear-positive pulmonary TB patients registered in 2004, receiving standard chemotherapy with known later clinical course counted at 8,563. Treatment success cases accounted for 78%, deaths 13%, and treatment defaulter 7.2%. Those whose treatment was started more than two years ago and still showing bacillary excretion in 2005 (supposed to be chronic bacillary excretors) counted at 480 (558 in 2004).

International comparison: The incidence rates in some developed countries (2004, the report of WHO) were 4.6 in Sweden, 4.9 in USA, 5.3 in Australia, 6.6 in Denmark, 7.3 in Germany, 8.3 in France, and 11.8 in UK. Japan (22.2) has a level twice to five times as high as those in these countries and about the same as that of USA in latter half of 1960s. In most of these Western countries, more than half of cases were foreign-born. In Japan, 92% of newly registered cases were of known nationality and foreigners were only 3.5% of them.

Conclusion: As described above, the status of TB in Japan has been improving slowly after declaration of TB emergency in July 1999. To attain the incidence rate of European and American level, being lower than 10, more than 20 years will be anticipated. Besides, such difficult problems as outbreaks of TB infection (see p. 257-263 of this issue), nosocomial infection, increase of severe cases with poor prognosis, and multi-drug resistant TB (see p. 263 of this issue) have emerged. For some time from now, medical professions and central or local governments should keep strong commitment to TB problems.

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