STAPHYLOCOCCAL INFECTIONS

Staphylococci are broadly classified as coagulase positive (Staph. aureus) or coagulase negative (Staph. epidermidis), based on their ability to produce a clumping factor (coagulase) to protect themselves against host defense.

High-risk factors for staphylococcal disease include: (a) impaired skin/mucosal barrier, e.g. trauma, surgery, burns, vascular access, shunts, (b) altered nasal flora after viral infections or prolonged antibiotics, and (c) immunodeficiency states.

Pathogenesis: Disease may result due to direct tissue invasion (localized disease) or via toxins produced by different strains, e.g. exfoliative toxins (staphylococcal scalded skin syndrome), enterotoxins (food poisoning), and TSS-1 (toxic shock syndrome).

Clinical spectrum: Staphylococci is the leading cause of superficial skin infections in children, apart from various localized or generalized serious infections (Table 10.7). Diagnosis rests on the culture from infected lesion. A positive skin/nasopharyngeal culture is of a little significance due to normal colonization.

TABLE 10.7: Clinical spectrum of staphylococcal infections

• Skin infections

- Focal: Impetigo, folliculitis, wound infection

- Staphylococcal scalded skin syndrome

• Respiratory infections

- Upper*: Otitis, sinusitis, bacterial tracheitis

- Lower: Pneumonia, empyema, pneumothorax

• Septicemia

• Metastatic lesions:

- Osteoarticular: osteomyelitis, arthritis

- CNS: Meningitis, brain abscess, epidural abscess

- GIT: Peritonitis, food poisoning

- Heart: Pericarditis, endocarditis

- Kidney*: Renal/perinephric abscess

- Muscles: Tropical myositis and muscle abscesses

*Tonsilopharyngitis and UTI is rare

Treatment includes specific antibiotic therapy and drainage of pus.

Methicillin-resistant Staph. aureus (MRSA) is an emerging problem in critically sick children, due to presence of a penicillin-binding protein, which is relatively resistant to #946;-lactam ring of antibiotics. Although methicillin is currently not available, the term 'MRSA' continues to be in use to denote organisms resistant to cloxacillin and other semisynthetic penicillins.

Prevention of staphylococcal infections in hospital requires: (a) strict hand-washing, with/without chlor- hexidine, (b) isolation of case or carrier, and (c) rational use of antibiotics.

Toxic-shock syndrome (TSS) is an acute multi-systemic disease due to an exotoxin TSS-1, usually caused by staphylococci phage type-I. Mostly seen in menstruating women due to use of infected tampoons, non-menstrual TSS has been reported following wound infection, nasal packing for epistaxis and invasive staphylococcal disease.

Clinically TSS is characterized by three major features: (i) sudden onset of high fever, (ii) severe hypotension/ shock and (iii) generalized erythematous rash after 24 hours of the onset of fever.

Important minor features include—(a) mucosal lesions, e.g. strawberry tongue, conjunctival congestion,

(b) vomiting/diarrhea, (c) severe myalgia, (d) altered sensor ium without focal signs, (e) liver/ renal abnor­malities, and (f) thrombocytopenia.

Diagnosis depends on presence of all major criteria and/ or minimum three minor criteria (mentioned above), after exclusion of other causes and negative blood culture. D/D includes streptococcal TSS and Kawasaki disease.

Treatment includes drainage of infected site, parenteral antibiotic therapy with vancomycin, and supportive treatment for shock and other complications.

Prognosis is poor in untreated cases.

Other staphylococcal disorders, staphylococcal scal­ded skin syndrome (SSSS) are discussed elsewhere (Ch25.6). Coagulase negative staphylococci (CONS), i.e. Staph. epidermidis, is a normal inhabitant of human skin, oropharynx and genital tract. Originally thought to be non-virulent, it is now known to cause serious nosocomial infections in susceptible children.

High-risk factors for CONS infections include: (a) presence of indwelling devices, e.g. shunts, catheters or prosthetic devices, etc., (b) post-operative infections, and

(c) immunocompromised states.

Clinical spectrum: CONS infections may be limited to occult bacteremia or present with site-related infections, e.g. CSF-shunt infection (commonest cause), urinary catheter-related UTI, dialysis catheter-related peritonitis or infective endocarditis in cases with prosthetic valves. Diagnosis rests on blood or shunt/catheter-tip culture, but should be differentiated from normal colonization. A CONS culture is considered as pathogenic if: (a) at least two cultures from same site at different times or different sites at same time are positive, or (b) patient is high-risk, i.e. newborn or has an in situ catheter.

Treatment: Vancomycin is the drug of choice for CONS, though the efficacy may be enhanced with addition of rifampicin or an aminoglycoside. Removal of suspected source, e.g. catheter is essential.

10.3