Acute rheumatic fever and poststreptococcal glomerulonephritis in an open population: comparative studies of epidemiology and bacteriology.

We conducted epidemiologic and bacteriologic studies of 104 cases of acute rheumatic fever (ARF) and 84 cases of poststreptococcal acute glomerulonephritis (AGN) occurring in the southeast health district of Santiago, Chile, between March 1978, and February 1982. The AGN cases were both postpharyngeal and postpyodermal in origin. Despite the fact that ARF and AGN were occurring in the same neighborhoods and among families of equivalent size and socioeconomic status, the pharyngeal isolation rates of group A streptococci were significantly lower among patients with ARF and their household contacts than among patients with AGN and their contacts. Moreover, the streptococcal throat colonization rates and geometric mean anti-streptolysin O titers were similar in ARF families and the families of noninfected controls. Streptococci of M-type 5, a highly rheumatogenic type, were isolated from three patients with ARF (representing 36% of group A isolates from this group) and one ARF contact but never from patients with AGN, control subjects, or their respective contacts. These observations suggest possible differences in the streptococcal milieus from which ARF and AGN cases emerge. The nature of such differences requires further exploration.