Reported cases of tuberculosis in Seattle & King County increased from 104 in 1999 to 127 in 2000. Although the number of cases reported in 2000 was 22% higher than that reported in 1999, Figure 1 shows that the trend of tuberculosis in Seattle & King County has been relatively stable over the past decade. Of the 127 TB cases, 68 (54%) were male and 59 (46%) were female; age at diagnosis ranged from 2 to 89 years. The majority of cases (79%) were born outside of the United States; only 21% were born in the U.S. Eight (6%) of the cases died; one was diagnosed post mortem, and seven died during the course of treatment.

The incidence rate of TB in residents of Seattle (14 cases/100,000) was more than three times that of residents of King County living outside of Seattle (4.2 cases/100,000). Analysis of cases by zip code of residence indicated that downtown Seattle and the neighborhoods immediately east and south of downtown Seattle (Georgetown and Rainier Valley) continued to have the highest rates of tuberculosis. These neighborhoods, home to 6% of county residents, were home to 30% of county TB cases, and had an aggregate incidence rate of TB of 34/100,000, almost 5 times that of Seattle & King County as a whole.

Birth in a geographic area where TB is endemic was again in 2000 the most important risk factor for TB, accounting for 100 cases (79%). Foreign-born cases had emigrated from 27 countries: 16 cases from Vietnam; 13 each from the Philippines and Ethiopia; 7 from Mexico; 5 from China and 3 from Eastern Europe, including countries of the former Soviet Union.

One striking difference between U.S.-born and foreign-born cases was the age at onset of tuberculosis. Figure 2 shows that foreign-born TB cases occurred at much younger ages, with the mode in the third decade of life. TB is striking these new residents in the productive, childbearing years of life, when there are usually young children in the household. In this setting it is particularly important that prompt, thorough contact investigations of cases of pulmonary TB be conducted in order to protect children from significant exposure.

The site of infection for 2000 TB cases was pulmonary for 81 cases (64%), both pulmonary and extra-pulmonary for 11 cases (9%), and extra-pulmonary for 35 (28%). Among pulmonary cases, 83 (90%) were culture-positive, and 39 (42%) were sputum smear-positive. Among the 46 total extra-pulmonary cases, 13 were lymphatic, 8 were pleural, 5 were bone/joint; 2 were miliary.

Drug susceptibility testing was performed on all 105 (83%) culture-positive cases. Nine isolates exhibited a significant level of drug resistance, eight of these from foreign-born cases. Seven isolates (7%) were resistant to isoniazid but susceptible to rifampin; none was resistant to rifampin alone. Two cases in immigrants from the Philippines and Mexico were resistant to both isoniazid and rifampin, meeting the definition for multi-drug resistant tuberculosis (MDR-TB). Significant drug resistance occurred in 8% (8/100) of foreign-born culture-positive cases and in 4% (1/27) of U.S.-born cases. The incidence of drug resistance in Seattle & King County TB cases has remained relatively stable in recent years. The level of resistance to TB drugs can be an important indicator of the quality of TB control in a community. A rising rate of drug resistance generally indicates suboptimal follow-up of patients and a low rate of completion of treatment, leading to MDR-TB and increased person-to-person spread of TB.

During 2000, the TB Control Program received 252 reports of suspected TB cases. Washington Law requires that patients with suspected TB be reported because important public health interventions may be indicated immediately, even before the diagnosis is certain. Reporting of suspected tuberculosis cases, therefore, is both an indicator of the awareness of TB among medical practitioners in Seattle & King County and an indicator of work burden for the TB Program Staff. Reported suspect TB cases often require consultation, contact investigations, and monitoring of clinical status, cultures, and compliance with treatment, even though in 2000 only half (127/252) of reported suspects proved to be actual cases of TB.