Streptococcal and enterococcal infections

Infection with Viridans Streptococci: Treatment Isolates from neutropenic patients with bacteremia are often resistant to penicillin; thus these patients should be treated presumptively with vancomycin until the results of susceptibility testing become available. Viridans streptococci isolated in other clinical settings usually are sensitive to penicillin. Abiotrophia Species (Nutritionally Variant Streptococci) Occasional isolates cultured from the blood of patients with endocarditis fail to grow when subcultured on solid media.

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Enterococci may be resistant to penicillins via two distinct mechanisms. The first is β-lactamase production (mediating resistance to penicillin and ampicillin), which has been reported for E. faecalis isolates from several locations in the United States and other countries. Because the amount of β-lactamase produced may be insufficient for detection by routine antibiotic susceptibility testing, isolates from serious infections should be screened specifically for βlactamase production with a chromogenic cephalosporin or another method.

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Group B Streptococcal Infection in Adults: Treatment GBS is less sensitive to penicillin than GAS, requiring somewhat higher doses. Adults with serious localized infections (pneumonia, pyelonephritis, abscess) should receive doses of ~12 million units of penicillin G daily; patients with endocarditis or meningitis should receive 18–24 million units per day in divided doses. Vancomycin is an acceptable alternative for penicillin-allergic patients.

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Streptococcal Toxic Shock Syndrome: Treatment In light of the possible role of pyrogenic exotoxins or other streptococcal toxins in streptococcal TSS, treatment with clindamycin has been advocated by some authorities (Table 130-3), who argue that, through its direct action on protein synthesis, clindamycin is more effective in rapidly terminating toxin production than penicillin—a cell-wall agent. Support for this view comes from studies of an experimental model of streptococcal myositis, in which mice given clindamycin had a higher rate of survival than those given penicillin.

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Infection in Neonates Two general types of GBS infection in infants are defined by the age of the patient at presentation. Early-onset infections occur within the first week of life, with a median age of 20 h at onset. Approximately half of these infants have signs of GBS disease at birth. The infection is acquired during or shortly before birth from the colonized maternal genital tract. Surveillance studies have shown that 5– 40% of women are vaginal or rectal carriers of GBS.

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Erysipelas is a streptococcal infection of the superficial dermis and consists of well-demarcated, erythematous, edematous, warm plaques Classic cases of erysipelas, with typical features, are almost always due to β-hemolytic streptococci, usually GAS and occasionally group C or G. Often, however, the appearance of streptococcal cellulitis is not sufficiently distinctive to permit a specific diagnosis on clinical grounds.

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Deep Soft-Tissue Infections: Treatment Once necrotizing fasciitis is suspected, early surgical exploration is both diagnostically and therapeutically indicated. Surgery reveals necrosis and inflammatory fluid tracking along the fascial planes above and between muscle groups, without involvement of the muscles themselves. The process usually extends beyond the area of clinical involvement, and extensive debridement is required. Drainage and debridement are central to the management of necrotizing fasciitis; antibiotic treatment is a useful adjunct (Table 130-3), but surgery is lifesaving.

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Asymptomatic Pharyngeal Colonization with Gas: Treatment When a carrier is transmitting infection to others, attempts to eradicate carriage are warranted. Data are limited on the best regimen to clear GAS after penicillin alone has failed. The combination of penicillin V (500 mg four times daily for 10 days) and rifampin (600 mg twice daily for the last 4 days) has been used to eliminate pharyngeal carriage. A 10-day course of oral vancomycin (250 mg four times daily) and rifampin (600 mg twice daily) has eradicated rectal colonization.

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Impetigo contagiosa is a superficial streptococcal or Staphylococcus aureus infection consisting of honey-colored crusts and erythematous weeping erosions. Occasionally, bullous lesions may be seen. (Courtesy of Mary Spraker, MD.) The classic presentation of impetigo usually poses little diagnostic difficulty. Cultures of impetiginous lesions often yield S. aureus as well as GAS. In almost all cases, streptococci are isolated initially and staphylococci appear later, presumably as secondary colonizing flora. In the past, penicillin was nearly always effective against these infections.

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Clinical Manifestations Pharyngitis Although seen in patients of all ages, GAS pharyngitis is one of the most common bacterial infections of childhood, accounting for 20–40% of all cases of exudative pharyngitis in children; it is rare among those under the age of 3. Younger children may manifest streptococcal infection with a syndrome of fever, malaise, and lymphadenopathy without exudative pharyngitis. Infection is acquired through contact with another individual carrying the organism.

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Gas Pharyngitis: Treatment In the usual course of uncomplicated streptococcal pharyngitis, symptoms resolve after 3–5 days. The course is shortened little by treatment, which is given primarily to prevent suppurative complications and ARF. Prevention of ARF depends on eradication of the organism from the pharynx, not simply on resolution of symptoms, and requires 10 days of penicillin treatment (Table 130-3). Erythromycin may be substituted for penicillin in cases of penicillin allergy.

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Group A Streptococci Lancefield's group A consists of a single species, S. pyogenes. As its species name implies, this organism is associated with a variety of suppurative infections. In addition, GAS can trigger the postinfectious syndromes of ARF (which is uniquely associated with S. pyogenes infection; Chap. 315) and PSGN (Chap. 277). Worldwide, GAS infections and their postinfectious sequelae (primarily ARF and rheumatic heart disease) account for an estimated 500,000 deaths per year.

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Harrison's Internal Medicine Chapter 130. Streptococcal and Enterococcal Infections Streptococcal and Enterococcal Infections: Introduction Many varieties of streptococci are found as part of the normal flora colonizing the human respiratory, gastrointestinal, and genitourinary tracts. Several species are important causes of human disease. Group A Streptococcus (GAS, S.

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