Seroprevalence of Streptococcal Inhibitor of Complement (SIC) suggests association of streptococcal infection with chronic kidney disease

BACKGROUND Group A streptococcus (GAS) is an etiological agent for the immune mediated sequela post streptococcal glomerulonephritis (PSGN). In some populations PSGN is recognized as a risk factor for chronic kidney disease (CKD) and end-stage renal disease (ESRD). It was found that a significantly greater proportion of subjects with past history of PSGN than without the history exhibited seroreactions to streptococcal antigens called streptococcal inhibitor of complement (SIC) and to distantly related SIC (DRS). These antigens are expressed by major PSGN-associated GAS types. We therefore predicted that in populations such as India, which is endemic for streptococcal diseases and which has high prevalence of CKD and ESRD, greater proportions of CKD and ESRD patients exhibit seroreaction to SIC and DRS than healthy controls. METHODS To test this we conducted a SIC and DRS seroprevalence study in subjects from Mumbai area. We recruited 100 CKD, 70 ESRD and 70 healthy individuals. RESULTS Nineteen and 35.7% of CKD and ESRD subjects respectively were SIC antibody-positive, whereas only 7% of healthy cohort was seropositive to SIC. Furthermore, significantly greater proportion of the ESRD patients than the CKD patients is seropositive to SIC (p=0.02; odds ratio 2.37). No association was found between the renal diseases and DRS-antibody-positivity. CONCLUSIONS Past infection with SIC-positive GAS is a risk factor for CKD and ESRD in Mumbai population. Furthermore, SIC seropositivity is predictive of poor prognosis of CKD patients.