Infection	Source patient's disease status	Status of exposed person	Regimen
Invasive group A streptococcal infection	Necrotizing streptococcal fasciitis from presentation until 48 hours after initiation of antibiotic	High-risk household contacts*	A single dose of penicillin G benzathine (600,000 units IM in patients weighing < 60 lb [27 kg] or 1,200,000 units IM in patients weighing = 60 lb)
				plus
			Rifampin (10 mg per kg twice daily orally, divided into two doses; maximum daily dosage: 600 mg) twice daily for four days
				or
			Clindamycin (20 mg per kg orally; maximum daily dosage: 900 mg) three times daily for 10 days
				or
			Azithromycin (Zithromax; 12 mg per kg orally; maximum daily dosage: 500 mg) daily for five days
Invasive meningococcal infection	From seven days before onset of illness until 24 hours after initiation of antibiotic	Any close contact regardless of vaccination status†	Ciprofloxacin (Cipro; a single dose of 500 mg orally)
				or
			Azithromycin (a single dose of 500 mg orally)
				or
			Ceftriaxone (Rocephin; a single dose of 250 mg IM)
				or
			Rifampin (600 mg orally, twice daily for two days)
			Begin antimicrobial chemoprophylaxis as early as possible, but no more than 14 days after exposure
Pertussis	Within 21 days of the onset of cough	All household and other close contacts regardless of vaccination status‡	Azithromycin (500 mg orally) on day 1, then 250 mg daily for four days
				or
			Clarithromycin (Biaxin; 500 mg orally) twice daily for10 days
				or
			Erythromycin (500 mg orally) four times daily for 14 days
				or
			Trimethoprim/sulfamethoxazole (160/800 mg orally) twice daily for seven to 14 days
Tetanus	After a tetanus-prone injury§	Any person with an uncertain or incomplete history of completing a three-dose primary series of tetanus toxoid–containing vaccine, or if the most recent dose was given ≥ 10 years ago (for minor and clean wounds) or ≥ five years ago (for puncture wounds or wounds contaminated with dirt)	Tetanus toxoid–containing vaccine (Td, Tdap, TT); add a single dose of tetanus immune globulin (250 units IM), except after minor and clean wounds, if it is unclear that the three-dose primary vaccination series has been completed||
Tuberculosis	Untreated active pulmonary or laryngeal tuberculosis	Every person at risk regardless of previous bacille Calmette-Guérin immunization or tuberculosis history	Tuberculin skin test or interferon-gamma release assay should be performed at baseline and at eight to 12 weeks after exposure
			If tuberculin skin test ≥ 5 mm or interferon assay is positive, for nine months treat with isoniazid plus vitamin B6