<prompt> True about Diptheria -Caused by Gram negative bacilliIncubation period 2-5 daysChemoprophylaxis is done with rifampicinAll  <response>: Ans. is b i.e.,Incubation period 2-5 days . Diptheria is caused by Gram positive bacilli, Corynebacterium diphtheriae . Incubation period of most common form of diphtheria faucial tonsiliopharyngeal diphtheria is 2-5 days. . For chemoprophylaxis erythromycin or penicillin are used. Previously immunized asymptomatic household contact should receive booster dose of diphtheria toxoid. Those not fully immunized but asymptomatic contacts should receive immunization for their age.---0.P. Ghai 7th221 Lifelong immunity is usually, but not always, acquired after disease or inapparent infection---health.vic.gov.au IDAES home blue book . So, child recovered from illness is already is immune. No active immunization is required. 