A herd immunity of over - % is considered necessary to prevent epidemic spread of diphtheria-

Ans. is 'd' i.e., 70% o A herd immunity of over 70% is considered necessary to prevent epidemic spread, but some believe that the critical level may be as high as 90%.Diphtheriao Diphtheria is an acute infectious disease caused by toxigenic strains of corynebacterium diphtheriae.o Source of infection - cases or carriers; carriers are common sources of infection, their ratio is estimated to be 95 carriers for 5 clinical cases.o Infective period-14-28 days from the onset of disease,o Age group-1 to 5 yearso Sex-Both sexeso Incubation period-2-6 dayso The period of infectivity may vary from 14 to 28 days from the onset of the disease, but carriers may remain infective for much longer period.o A case or carrier may be considered non-communicable when at least 2 cultures properly obtained from nose and throat, 24 hours apart, are negative for diphtheria bacilli.Control of diphtheriao Control diphtheria requiresControl in cases and carrierControl for contacts (prophylaxis for contact)Prophylaxis for community ->> by vaccinationControl in cases and carrier1) Early diagnosis-By nose & throat examination and culture.2) Isolation-For at least 14 days or until proved free of infection, i.e. at least 2 consecutive nose and throat swabs, taken 24 hours apart, should be negative before terminating isolation.Treatmenti) Cases-Diphtheria antitoxin plus penicillin or erythromycin.ii) Carrier-Erythromycin