▁children ▁( 5 0 ▁to ▁ 8 0 % ▁of ▁S . ▁py ogen es ▁in fection ) ▁with ▁no ▁known ▁risk ▁factors . ▁The ▁rates ▁of ▁scar let ▁fe ver ▁in ▁UK ▁was ▁usually ▁ 4 ▁in ▁ 1 0 0 , 0 0 0 ▁population , ▁however , ▁in ▁ 2 0 1 4 , ▁the ▁rates ▁had ▁ris en ▁to ▁ 4 9 ▁per ▁ 1 0 0 , 0 0 0 ▁population . ▁R he um atic ▁fe ver ▁and ▁r he um atic ▁heart ▁disease ▁( R HD ) ▁usually ▁occurs ▁at ▁ 2 ▁to ▁ 3 ▁weeks ▁after ▁the ▁thro at ▁in fection , ▁which ▁is ▁more ▁common ▁among ▁the ▁imp over ished ▁people ▁in ▁developing ▁countries . ▁From ▁ 1 9 6 7 ▁to ▁ 1 9 9 6 , ▁the ▁global ▁mean ▁inc idence ▁of ▁r he um atic ▁fe ver ▁and ▁R HD ▁was ▁ 1 9 ▁per ▁ 1 0 0 , 0 0 0 ▁with ▁the ▁highest ▁inc idence ▁at ▁ 5 1 ▁per ▁ 1 0 0 , 0 0 0 . ▁ ▁Mat ernal ▁S . ▁py ogen es ▁in fection ▁usually ▁happens ▁in ▁late ▁pre gn ancy ; ▁at ▁more ▁than ▁ 3 0 ▁weeks ▁of ▁gest ation ▁to ▁four ▁weeks ▁post ▁part um , ▁which ▁accounts ▁for ▁ 2 ▁to ▁ 4 % ▁of ▁all ▁the ▁S . ▁py ogen es ▁in fe ctions . ▁This ▁represents ▁ 2 0 ▁to ▁ 1 0 0 ▁times ▁increase ▁in