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INTRODUCTION

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The bacterium Arcanobacterium was first described in 1946 as a pathogen causing pharyngitis and cutaneous infections in US service members and people in the South Pacific. Arcanobacterium means “secretive bacteria.” Arcanobacterium haemolyticum is the most well-known species of Arcanobacterium affecting humans.

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EPIDEMIOLOGY AND PATHOGENESIS

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A haemolyticum can be isolated from approximately 0.4% of adults in the United States presenting with pharyngitis. This pleomorphic, nonsporulating, hemolytic, catalase-negative, gram-positive (sometimes gram-variable) bacillus resembles Corynebacterium pyogenes and is a facultative anaerobe as well as non–acid fast. Humans are the main environmental reservoir, but Arcanobacterium is not part of the normal respiratory tract flora. Disease is suspected to be spread from person to person by respiratory droplet. The incubation period is unknown.

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A haemolyticum is responsible for up to 2% to 2.5% of bacterial pharyngitis by culture in the United States as well as other countries. This bacterium appears to cause disease most commonly in those 10 to 30 years of age, with the maximum incidence occurring in those 15 to 18 years of age. There appears to be no difference in incidence between men and women or among different races.

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Although the mechanism for adherence of Arcanobacterium to pharyngeal mucosa remains unknown, A haemolyticum can liberate toxins, including a dermonecrotic toxin, using a mechanism similar to the production of erythrogenic toxin by group A β-hemolytic streptococci (GABHS).

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CLINICAL MANIFESTATIONS

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Presentation of disease caused by A haemolyticum is similar to GABHS pharyngitis, with fever, pharyngeal exudate, and lymphadenopathy, but palatal petechiae and a strawberry tongue are usually absent. A sore throat occurs in 97% to 100% and a patchy gray to white exudate in 70% of patients with A haemolyticum infection; however, fever and lymphadenopathy occur in only 50% of patients with pharyngitis. An exanthema, described only in patients with pharyngitis, develops 1 to 4 days after the symptoms of sore throat begin. This exanthema, which may be pruritic in up to 33% of patients, includes the extensor surfaces of the extremities and spreads centrally. The face, palms of the hands, and soles of the feet are not typically involved. Other forms of rash that occur include scarlatiniform and maculopapular. Some form of rash occurs in up to 75% of patients with A haemolyticum pharyngitis. Nonsuppurative sequelae have not been reported following pharyngitis caused by A haemolyticum.

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Infections of the skin caused by A haemolyticum, especially chronic ulcerations, occur mainly in tropical countries. Invasive infections, including brain abscess, endocarditis, meningitis, osteomyelitis, pneumonia, pyogenic arthritis, and sepsis, have been reported. A haemolyticum can be a rare cause of mortality, most often associated with endocarditis. Co-infection with Fusobacterium necrophorum can occur in cases of Lemierre disease. Severe, invasive disease occurs most frequently among immunocompromised hosts.

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DIAGNOSIS

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Adolescents with clinical findings typical for A haemolyticum pharyngitis and ...

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