infectious diseases
Staphylococcal Infections
Diagnosis of Staphylococcal Infections
Gram stain and culture Diagnosis of staphylococcal infections is by Gram stain and culture of infected material. Susceptibility tests should be done because methicillin-resistant organisms are now common and require alternative therapy. Whenstaphylococcal scalded skin syndromeis suspected, cultures should be obtained from blood, urine, the nasopharynx, the umbilicus, abnormal skin, or any suspected focus of infection; the intact bullae are sterile. Although the diagnosis is usually clinical, a biopsy of the affected skin may help confirm the diagnosis. Staphylococcal food poisoningis usually suspected because of case clustering (eg, within a family, attendees of a social gathering, or customers of a restaurant). Confirmation (typically by the health department) entails isolating staphylococci from suspect food and sometimes testing for enterotoxins. Inosteomyelitis,x-ray changes may not be apparent for 10 to 14 days, and bone rarefaction and periosteal reaction may not be detected for even longer. Abnormalities in MRI, CT, or radionuclide bone scans are often apparent earlier. Bone biopsy (open or percutaneous) should be done for pathogen identification and susceptibility testing. Some institutions that have a high incidence of methicillin-resistantS. aureus(MRSA) nosocomial infections routinely screen admitted patients for MRSA (active surveillance) by using rapid laboratory techniques to evaluate nasal swab specimens. Some institutions screen only high-risk patients (eg, those who are admitted to the intensive care unit, who have had previous MRSA infection, or who are about to undergo vascular, orthopedic, or cardiac surgery). Quick identification of MRSA does the following: Allows carriers to be placed in contact isolation and, when preoperative Prevention of Surgical Infections against skin organisms is required, to be given Decreases the spread of MRSA May decrease the incidence of nosocomial infections with MRSA In patients with pneumonia, polymerase chain reaction (PCR) testing for MRSA colonization in the nares has been shown to have a negative predictive value of > 95% for MRSA lung infection and may therefore be useful in antibiotic management. 