Non–Group A or B Streptococci

Chapter 178 Non–Group A or B Streptococci

The genus Streptococcus comprises >30 species. Streptococcus pneumoniae (Chapter 175), group A streptococcus (Chapter 176), and group B streptococcus (Chapter 177) are the most common causes of human streptococcal infections. The β-hemolytic streptococci of Lancefield groups C to H and K to V and the α-hemolytic streptococci that cannot be classified within a Lancefield group (the viridans streptococci) commonly colonize intact body surfaces (the pharynx, skin, gastrointestinal tract, genitourinary tract) and also cause infections in humans (see Table 178-1 on the Nelson Textbook of Pediatrics website at www.expertconsult.com ). Of the non–group A β-hemolytic streptococci, groups C and G streptococcus are the most frequent cause of human disease. The enterococci were once classified among the group D streptococci but are now a separate genus, Enterococcus (Chapter 179).

Group C streptococcus is a much more common cause of infection in animals than in humans. Humans infected with this organism often have had some animal contact. Both group C and group G streptococcus often can be part of the normal human flora of the nasopharynx, skin, and genital tract. Group C streptococcus can be cultured from the umbilicus of asymptomatic newborns and from routine puerperal vaginal cultures. Group G streptococcus also can be cultured from the gastrointestinal tract. Because of the relatively low virulence of group C and group G streptococci, most humans infected with either of these organisms have some underlying medical disorder (diabetes mellitus, malignancy, alcohol abuse, immunosuppression).

The clinical features of both group C and group G streptococcal pharyngitis are similar to those of group A streptococcal pharyngitis with fever, mild to moderate sore throat, pharyngeal exudate, and cervical lymphadenitis. Group C streptococcus is a relatively common cause of acute pharyngitis among college students and among adults who come to an emergency department. In addition to endemic pharyngitis, group C streptococcus can cause epidemic food-borne pharyngitis after ingestion of contaminated products, such as unpasteurized cow’s milk. Family and school outbreaks of group C streptococcal pharyngitis have also been described. Group C streptococcus has been reported as an uncommon cause of a number of other infections, including skin and soft tissue infections, septic arthritis, osteomyelitis, pneumonitis, infective endocarditis, bacteremia and septicemia, meningitis, epiglottitis, pericarditis, urinary tract infections, and sinusitis. Group C streptococcus also has been associated with epidemic and nonepidemic cases of puerperal sepsis and endometritis; there may be an association between group C streptococcus and reactive arthritis, as well as a toxic shock–like syndrome.

Even though there have been several well-documented food-borne outbreaks of group G streptococcal pharyngitis, the etiologic role of group G streptococcus in acute, endemic pharyngitis remains unclear. A community-wide respiratory outbreak of group G streptococcal pharyngitis in a pediatric population was described in which group G streptococcus was isolated from 56 of 222 (25%) consecutive children with acute pharyngitis seen at a private pediatric office. Results of DNA fingerprinting of the group G streptococcal isolates suggested that 75% of these were the same strain. The patients with group G streptococcal pharyngitis were comparable to those with group A streptococcal pharyngitis with respect to clinical findings, antistreptolysin O titer response, and clinical response to antibiotic therapy. These findings suggested that antibiotic therapy may have an impact on the clinical course of group G streptococcal pharyngitis.

Group G streptococcus has been reported to be an uncommon cause of puerperal sepsis and a neonatal infection that is clinically similar to early-onset group B streptococcal disease. Other infections occasionally caused by group G streptococcus include bacteremia, endocarditis, septic arthritis, osteomyelitis, pneumonia, erysipelas and other skin and soft tissue infections, and meningitis. Group G streptococcus has been associated with a toxic shock–like syndrome.

Acute rheumatic fever has not been described as a complication of either group C or group G streptococcal pharyngitis. There have been reports attempting to link acute glomerulonephritis with group G streptococcal pharyngitis; the evidence is anecdotal, and a causal relationship has not been established. Acute glomerulonephritis has been reported as a complication of group C streptococcal pharyngitis; it is extremely unusual. Therefore, the primary reason to identify either group C or group G streptococcus as the etiologic agent of acute pharyngitis is to initiate antibiotic therapy that may reduce the clinical impact of the illness. There is currently no convincing evidence from controlled studies of a clinical response to antibiotic therapy in patients with acute pharyngitis and either group C or group G streptococcus isolated from their upper respiratory tracts.

Penicillin is the antibiotic of choice for treating infections due to either group C or group G streptococcal infections. Pharyngitis usually is treated in a similar manner to group A streptococcal upper respiratory infections, whereas more severe infections require parenteral therapy.

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