SPREAD OF TUBERCULOSIS WITHIN FAMILIES

Study of the spread of latent tuberculous infection in families has been undertaken with the purpose of determining its relation to manifest disease. This study has shown that prolonged exposure to open tuberculosis causes tuberculous infection of all members of the household, and has furnished information by means of which the appearance of manifest tuberculosis in many instances may be predicted. Routine study of the exposed family as a whole is essential to the effective treatment and control of the disease. For convenience the term latent tuberculosis has been applied to all forms of tuberculosis that do not manifest themselves by symptoms or physical signs evident to the patient or to the physician. During 1923-1924, approximately 100 families came under observation, and during the subsequent three years the progress of the disease in them has been followed. During 1924-1925, approximately 250 more families have been included in the study, and