5. Characteristics of the disease

Among 34 countries with information on the new or recurrent status of the cases (Table 4) , an overall proportion of 10% of recurrent cases was reported among a total number of 226 785 cases. The proportion varied from 0% in Iceland, Malta and San Marino (all reporting less than 30 cases) to 23% in Norway (median 8%). The proportion of recurrent cases differed slightly between Group 1 and Group 2 countries. It varied from 3% to 23% in Group 1 (median 9.5%) and from 2% to 17% in Group 2 (median 8%).

According to age, the proportion of recurrent cases was small below 15 years of age (less than 2%), increased with age up to a maximum proportion of 15% in the group 55-64 and then decreased slightly to 14% in patients over 64 years of age. This trend appeared to result from different patterns: a proportion of recurrent cases increasing steadily with age to a maximum in patients over 64 in Group 1 countries, and a maximum proportion of recurrent cases in patients aged 45 to 64 in Group 2 countries. These differences might result from misclassification of cases in older patients due to difficulties in recalling past episodes of tuberculosis. However, it is difficult to interpret differences in proportions of recurrent cases because of between-country differences in definitions of recurrence.

Thirty-two countries documented the site of the disease for all incident (new and recurrent) cases (N=135 743), 22 using the pulmonary and 10 the respiratory classification (Table 5). Among the 22 countries using the pulmonary classification, 80% of the cases were reported as having pulmonary tuberculosis, alone or associated with extra-pulmonary site. The proportion varied by country from 42% to 100%. Eighteen of the 22 countries reported results of the sputum smear examination. Among the 67 709 cases notified in these 18 countries, the proportion reported as sputum smear positive was 40%, ranging by country from 17% to 50% (excluding San Marino). Sputum smear positive cases represented 49% of the cases reported with pulmonary tuberculosis. The 10 countries using the respiratory classification reported 90% of their cases as having respiratory tuberculosis, alone or associated with extra-respiratory site. The proportion varied from 65% in Albania to 95% in Turkey. Six of these countries reported results of sputum smear examination, among which 31% of the patients were reported as smear positive, i.e. 35% of the respiratory cases.

Six countries reported the site of the disease for new cases only (N=98 056), all using the respiratory classification (Table 6). The proportion of cases with respiratory tuberculosis was 93% in those countries. Three countries reported sputum smear results in their patients, among which 35% of the cases were smear positive.

The site of the disease differed by age group. The proportion of cases having extra-pulmonary tuberculosis was highest in children (36% in children under five, 41% in the group aged 5 to 14), decreased with age (25% in the 15-24 group, 20% in the 25-34 group, 17% between 35 and 64 years of age) then increased again to 20% in patients over 64. Among countries using the respiratory classification of the disease, the proportion of cases with extra-respiratory tuberculosis was also highest in children, was lowest (8%) in the 15 to 24 year-old patients then increased again to 15% in patients over 64 years of age.

Detailed description of the sites of the disease was possible for 10 countries reporting on both the major and the minor site for their 49 379 cases. These countries were both from Group 1 and Group 2. Among a total number of 51 101 sites reported in these patients (1.03 site per patient), the pulmonary localisation accounted for 82%. Other sites involved were, by decreasing order of frequency : pleural localisation (9%), intra-thoracic lymphatic, extra-thoracic lymphatic and genito-urinary localisation (2% respectively), other sites representing 1% or less of the sites involved. Disseminated tuberculosis accounted for 431 sites (1%), including 238 associated with pulmonary tuberculosis (this association includes miliary tuberculosis), and 193 not involving the lung parenchyma. Tuberculosis of the spine, tuberculous meningitis, other sites of the central nervous system, peritoneal and digestive sites were reported rarely and mainly as a single site of disease.

The association of sites in the same patient is described for children under five and for other patients. Overall, only 4% of the patients had more than one site involved: 3% had pulmonary tuberculosis associated with an extra-pulmonary localisation. Among these patients, the sites most frequently involved were the pleural (49%), the intra-thoracic lymphatic (24%) and the disseminated (13%) sites. Two or more extra-pulmonary sites were involved in 1% of the patients. The association of sites was more frequent in children under five (39%) than in other patients (4%) : most of these associations concerned a pulmonary together with an extra-pulmonary site, which are the sites usually involved in primary tuberculosis. A unique extra-pulmonary site was more frequent in children under five (34%) than in other patients (14%).

Information on bacteriological confirmation of the cases was available on all new and recurrent cases (N=81 764) in 27 countries, 9 using the recommended standard for confirmation, i.e. the positivity of the culture, and 18 requiring either one of the culture or the sputum smear positivity for confirmation (Table 7). In the first group, the proportion of cases confirmed by culture was 55%, varying from 44% in Hungary to 82% in Sweden. In the second group, the overall proportion of cases confirmed by culture or by sputum smear examination was 52%, varying from 28% in Uzbekistan to 91% in Denmark (excluding San Marino).

In the seven countries providing information on bacteriological confirmation for new cases only (Table 8), 43% of the 98 995 cases were bacteriologically confirmed.

In the 17 countries providing individual data, culture was reported to have been performed on 86% of the 54 896 cases. This proportion varied from 52% in the Netherlands and Italy to 100% in Poland. The proportion of total cases with positive culture was 44%, ranging from 30% in Estonia to 90% in Denmark. The proportion of cases confirmed by culture was more than two fold higher for pulmonary cases than for extra-pulmonary cases (48% versus 22%). In the 14 countries reporting on both culture and smear results, the proportion of cases with pulmonary localisation and positivity on both culture and sputum smear was low: 24% of the total cases (29% of the pulmonary cases). It was lower than the 39% of cases reported as sputum smear positive irrespective of culture results. Given the number of bacilli that must be present in the sputum in order for the smear examination to be positive, one would expect the culture to be positive in smear positive cases. Sputum smear positive cases without culture confirmation either had a culture performed but results were unknown (59%), or were reported as culture negative (16%) , as not having had a culture performed (15%) or with no information (10%).