NAME: Staphylococcus aureus
SYNONYM OR CROSS REFERENCE: MRSA (methicillin-resistant Staphylococcus aureus), MSSA (methicillin-susceptive (or sensitive) Staphylococcus aureus), VISA (vancomycin-intermediate Staphylococcus aureus), hVISA (heteroresistant vancomycin-intermediate Staphylococcus aureus), VRSA (vancomycin-resistant Staphylococcus aureus), staph infection, staphylococcus infection, impetigo, toxic shock syndrome.
CHARACTERISTICS: Staphylococcus aureus are Gram-positive, catalase positive cocci belonging to the Staphylococcaceae family Footnote 1, Footnote 2. They are approximately 0.5-1.5 µm in diameter, nonmotile, non-spore-forming, facultative anaerobes (with the exception of S. aureus anaerobius) that usually form in clusters. Many strains produce staphylococcal enterotoxins, the superantigen toxic shock syndrome toxin (TSST-1), and exfoliative toxins. Staphylococcus aureus are part of human flora, and are primarily found in the nose and skin Footnote 3.
PATHOGENICITY/TOXICITY: Staphylococcus aureus is an opportunistic pathogen that can cause a variety of self-limiting to life-threatening diseases in humans Footnote 2. The bacteria are a leading cause of food poisoning, resulting from the consumption of food contaminated with enterotoxins Footnote 4. Staphylococcal food intoxication involves rapid onset of nausea, vomiting, abdominal pain, cramps, and diarrhea Footnote 2, Footnote 4. Symptoms usually resolve after 24 hours Footnote 4. Animal bites can result in local infections, cellulitis, erythema, tenderness, mild fever, adenopathy, and lymphangitis (rarely) Footnote 5. Scalded skin syndrome is caused by exfoliative toxins secreted on the epidermis and mostly affects neonates and young children Footnote 2. Other skin conditions caused by Staphylococcal exfoliative toxins include blisters, skin loss, pimples, furuncles, impetigo, folliculitis, abscesses, poor temperature control, fluid loss, and secondary infection Footnote 2, Footnote 4, Footnote 6, Footnote 7. S. aureus can also cause necrotizing fasciitis in immunocompromised individuals, although this is very rare Footnote 8. Necrotizing fasciitis is life-threatening and causes severe morbidity.
Certain strains of S. aureus produce the superantigen TSST-1, which is responsible for 75% of toxic shock syndrome (TSS) cases Footnote 2. The clinical presentation of TSS is severe and acute symptoms include high fever, vascular collapse, vomiting, diarrhea, myalgia, hypotension, erythematous rash, desquamation, and involvement of at least 3 organs Footnote 2, Footnote 9, Footnote 10. Mortality is very high and death can occur within 2 hours Footnote 9. Toxic shock syndrome is associated with vaginal colonization with toxin-producing S. aureus during menstruation, complications with staphylococcal infection at other sites, or complications of surgical procedures Footnote 10. Deep infections include endocarditis, peritonitis, necrotizing pneumonia, bacteremia, meningitis, osteomyelitis, septic arthritis, and infections of bones, joints and organs Footnote 2, Footnote 6, Footnote 7.
EPIDEMIOLOGY: Worldwide distribution. Staphylococcus aureus is one of the most common causes of skin, soft-tissue, and nosocomial infection Footnote 7. Rates of infection in community settings are increasing Footnote 7, Footnote 11. Residents of nursing homes are also at an increased risk of acquiring MRSA Footnote 12. Around 20% of individuals are persistent carriers of Staphylococcus aureus, about 60% are intermittent carriers, and approximately 20% rarely carry it Footnote 3. Children are more likely to be persistent carriers of the bacteria Footnote 3. Young women are at a higher risk for toxic shock syndrome Footnote 10.
HOST RANGE: Humans, wild and domestic animals, including cows Footnote 13.
INFECTIOUS DOSE: At least 100,000 organisms in humans Footnote 14.
MODE OF TRANSMISSION: Ingestion of food containing enterotoxins Footnote 4. Vertical transmission during vaginal delivery is uncommon Footnote 15. Person-to-person transmission occurs through contact with a purulent lesion or with a carrier Footnote 3. Unsanitary conditions and crowded community settings increase exposure to S. aureus Footnote 16. Infection may be spread from person-to-person through health care workers or patients Footnote 3. Nasal colonization can lead to auto-infection Footnote 17.
INCUBATION PERIOD: Onset of symptoms after consuming contaminated food is usually 30 minutes to 8 hours Footnote 4. Colonies of S. aureus can be carried for an undetermined amount of time; some individuals may carry it chronically, and some may carry it intermittently Footnote 3.
COMMUNICABILITY: Communicable period is as long as a purulent lesion is present or carrier state persists.
RESERVOIR: Staphylococcus aureus is found in humans in the nose, groin, axillae, perineal area (males), mucous membranes, the mouth, mammary glands, hair, and the intestinal, genitourinary and upper respiratory tracts Footnote 2, Footnote 4, Footnote 18. Many animals act as reservoirs, particularly cows with infected udders Footnote 13.
ZOONOSIS: Yes, through direct or indirect contact with an infected animal Footnote 5.
DRUG SUSCEPTIBILITY: Antibiotics such as cloxacillin and cephalexin are commonly used to treat staph infections Footnote 19. Vancomycin which is administered intravenously is used to treat MRSA Footnote 20.
DRUG RESISTANCE: Many strains of Staphylococcus aureus have increasing resistance to multiple antibiotic classes Footnote 6. Methicillin resistant strains are common causes of nosocomial infection Footnote 21. Increasing resistance to vancomycin is being documented in many hospitals Footnote 6.
SUSCEPTIBILITY TO DISINFECTANTS: Susceptible to 70% ethanol, clorhexidine, 1% sodium hypochlorite, 2% glutaraldehyde, 0.25% benzalkonium chloride, and formaldehyde Footnote 12, Footnote 22, Footnote 23.
PHYSICAL INACTIVATION: Staphylococcus aureus can grow in a pH of 4.2 to 9.3 and in salt concentrations of up to 15% Footnote 4. Enterotoxins are resistant to temperatures that would destroy the bacilli Footnote 4. Sensitive to dry heat treatment of 160-170oC for at least an hour, but not to moist heat treatment Footnote 24.
SURVIVAL OUTSIDE HOST: Survives on carcasses and organs (up to 42 days), floors (less than 7 days), glass (46 hours), sunlight (17 hours), UV (7 hours), meat products (60 days), coins (up to 7 days), skin (30 minutes to 38 days) (citation needed). Depending on colony size, S. aureus can survive on fabrics from days to months Footnote 25.
SURVEILLANCE: Monitor for symptoms. In outbreak settings, food poisoning can be diagnosed on clinical grounds with food cultured for S. aureus Footnote 2. Toxic shock syndrome can be indicated with a clinical diagnosis and isolation of S. aureus strain, TSST-1, or enterotoxins B or C. This can be achieved using ELISA, reverse passive latex agglutination, or PCR. Scalded skin syndrome can be diagnosed clinically, with presence of Nikolsky’s sign and identification of S. aureus retrieved from the infection site. Bacteremia and deep site infections are confirmed with direct microscopic examination of clinical specimen.
Note: All diagnostic methods are not necessarily available in all countries.
FIRST AID/TREATMENT: Treatment of abscesses usually does not need antibiotic therapy; appropriate drainage is usually sufficient Footnote 6. Proper antibiotic therapy is required for more serious infections.
IMMUNIZATION: None Footnote 2.
PROPHYLAXIS: Elimination of nasal carriage by using topical mupirocin also eliminates hand carriage Footnote 3.
LABORATORY-ACQUIRED INFECTIONS: 29 reported cases as of 1973, with 1 death Footnote 26.
PRIMARY HAZARDS: Trauma of cutaneous barrier, parenteral inoculation, direct implantation of medical devices (i.e. indwelling catheters and IVs), ingestion of infected material, and contact with aerosols Footnote 2, Footnote 4, Footnote 18.
SPECIAL HAZARDS: Contaminated request forms that have been wrapped around specimen containers Footnote 21. Direct contact with open cuts and lesions of skin.
RISK GROUP CLASSIFICATION: Risk Group 2 Footnote 27.
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures.
PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable. Eye protection must be used where there is a known or potential risk of exposure to splashes Footnote 28.
OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC). The use of needles, syringes, and other sharp objects should be strictly limited. Additional precautions should be considered with work involving animals or large scale activities Footnote 28.
SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply an appropriate disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up.
DISPOSAL: Decontaminate all wastes that contain or have come in contact with the infectious organism before disposing by autoclave, chemical disinfection, gamma irradiation, or incineration.
STORAGE: The infectious agent should be stored in leak-proof containers that are appropriately labelled.
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: December 2011
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Public Health Agency of Canada, 2011