Demographic risk factors and lymphocyte populations in patients with tuberculosis and their healthy contacts

SETTING: Campania, a southern region of Italy, and the Institute of Respiratory Diseases, Monaldi Hospital, University 'Federico II', Naples. OBJECTIVE: To evaluate clinical and socio-demographic risk factors for tuberculosis (TB) infection and/ or disease. Peripheral blood lymphocytes from a subcohort of 19 patients and 53 contacts were studied by flow cytometry. DESIGN: A prospective study among patients with newly diagnosed pulmonary tuberculosis and their close contacts. RESULTS: A total of 90 patients and 277 contacts were enrolled. The prevalence of infection was 45% (95%CI 39-51%) among contacts. Age, sex, delay in diagnosis and treatment, cavitation on chest radiograph, cough, unwillingness to cover the mouth, and volume of air shared by close contacts and patients were investigated as potential risk factors for infection. Only delay in diagnosis of cases remained independently associated with an increased risk of infection (P < 0.0002), and hemoptysis was the only factor capable of reducing the delay significantly. The CD8(+)CD28(+) cytotoxic subset was significantly diminished in the patients (P < 0.001), whereas the CD8(+)CD28(-) and CD8(+)CD57(+) (suppressor and NK-like subsets) were elevated (P < 0.001 and P = 0.04). CONCLUSIONS: These data show that delay in diagnosis of cases is a crucial factor for tuberculosis and that cytotoxic CD8(+) cells play a primary role in immune response to tuberculosis.