<prompt> True statement regarding diptheria is :It can be diagnosed by demonstration of antibodies by ELISAImmunization prevents carriers stateTreatment of contacts is not indicatedIron has critical value in the production of toxin  <response>: Diagnosis of Diptheriai. Isolation by culture :Swabs are inoculated on : Loefflers serum slope growth is rapid : for rapid diagnosis. Tellurite blood agar growth is delayed but it is particularly important in isolation of bacilli from convalescent, contacts, carriers : Selective media. Blood agar for differentiating staphylococcal and streptococal pharyngitis. convalescent, contacts, carriers : Selective media. Blood agar for differentiating staphylococcal and streptococal pharyngitis.ii. Demonstration of toxicity of isolated strain :In vivo test done by infected broth emulsion of culture subacutaneously and intracutaneously into guinea pigs.In vitro test Eleks gel precipitation test and tissue culture test on agar overlay of cell culture monolayer.Control of Diptheriai. Cases Antitoxin penicillin or erythromycinPark 19e, p 137ii. Carriers Erythromyciniii. Contacts a. When primary immunization or booster dose was received within the previous 2 years.No further treatment.b. When primary immunization or booster dose was received more than 2 years ago.Only a booster dose of diphtheria toxoid.c. Non immunized close contacts :Prophylatic penicillin or erythromycin1000 - 2000 units of diphtheria antitoxinActive immunization against diphtheria.iv. Community Only effective control is by active immunization with diphtheria toxoid of all infants with subsequent booster doses every 10 years thereafter.Remember : Vaccine being a toxoid is not directed against organism and hence immunization does not prevent carrier state which is due to organism not due to toxin. 