1. The disease
2. Laboratory testing
3. Public health response
4. References
5. Further information and resources

1. The disease

Infectious agent

Staphylococcus aureus (commonly known as golden staph) are bacteria commonly found on the skin and in the nose of people. Staph carriage is usually harmless but sometimes it can cause skin infections, abscesses, pneumonia, osteomyelitis and bacteraemia. Some strains of staph are resistant to the antibiotic methicillin and other antibiotics that were used in the past to treat infections. These are known as methicillin resistant Staphylococcus aureus (MRSA).

MRSA has previously been associated with health care facilities but it has recently been recognised that there are MRSA strains that can cause infections in otherwise healthy individuals. These strains are distinct from hospital strains and are referred to as community-acquired MRSA (CaMRSA).

Mode of transmission

The bacteria are easily shed from the skin and infected draining wounds. Purulent discharge contains high concentrations of the organism and is the most common source. Person-to-person transmission occurs through contact with a purulent wound through broken skin.

Infectious period

Because people can be colonised for months prior to infection, the incubation period is not well defined.

Clinical presentations and outcomes

MRSA infections in the community usually manifest as skin infections such as pimples, boils, impetigo, furuncles, carbuncles, and abscesses. Septicaemia and pneumonia or osteomyelitis can also occur.

2. Laboratory testing

Infection with MRSA is confirmed:

• isolation of Staphylococcus aureus from a purulent lesion or from the blood, urine, peritoneal fluid, or cerebrospinal fluid of a patient with clinical signs of infection
• and which demonstrates resistance to methicillin and all other ß-lactam antibiotics.

3. Public health response

MRSA is not a notifiable disease. Clinicians are encouraged to report to the public health unit if clusters of infection occur (i.e. two or more related cases). The response to a cluster should be carried out in collaboration with the cases' health carers. Treatment of individual cases is the responsibility of the doctor.

An investigation is required if ongoing transmission is occurring in a well-defined, closely-associated cohort (such as a household, classroom, childcare centre or sporting group). The response to an outbreak of skin and soft tissue infections due to MRSA will vary and may be influenced by the number of cases, the severity, the setting, and further public health risk. The following 10 steps provide a systematic approach to CaMRSA outbreak investigations.

Establish the existence of an outbreak

A CaMRSA outbreak is defined two or more related cases of CaMRSA skin and soft tissue infections in a well defined, closely associated cohort. There are no data routinely collected on the incidence of skin and soft tissue infections (due to any cause).

Verify the diagnosis

It is important to make sure that the group of possible outbreak cases is actually experiencing the same illness. This is especially important for an outbreak defined by a symptom, such as skin infection, as there are many possible causes. To confirm CaMRSA infection, a wound swab should be taken for microscopy and culture. Alert the laboratory of the outbreak to guide testing procedures and to determine the estimated time frame for results.

Determining the strain involved in an outbreak, through molecular typing, can provide evidence of related cases and may provide insight to transmissibility and potential for environmental spread. Testing should be determined in consultation with microbiological experts and infectious diseases specialists where available.

Define and identify cases

A case definition should be developed specifying time, person and place. Identify the group of people who may have been exposed to CaMRSA. Cases should be interviewed about risk factors for illness including:

• contact with a person with skin infections
• attending child care
• participating in contact sports
• living in a large household
• history of wound infections
• employment in a healthcare facility
• IV drug use
• prior hospitalisation
• co-morbidities (e.g. diabetes)
• time spent in prison.

Perform descriptive epidemiology

Describe the case data in terms of time, place and person and draw an epidemiological curve to display the number of cases by day of onset. Develop a line-listing of cases, including:

• case identifiers
• age, sex, place of residence
• relevant demographic factors including Aboriginality and ethnicity
• presence of skin lesions
• date of onset and symptoms
• previous infection
• date of laboratory confirmed MRSA
• previous hospital admission (surgical wounds, invasive devices, other procedures
• relevant exposures.

Determine who is at risk

Consider the source of infection and the usual mode of transmission based on analysis of the data collected. Identify potential facilitators of ongoing infection and barriers to infection control.

Develop hypothesis

Consider the source of the illness and the usual mode of transmission based on analysis of the data gathered on the place, time and personal characteristics of the cases, and exposure histories.

Evaluate hypothesis

Consider whether an analytical study (usually a cohort or a case-control study to compare exposures, behaviours associated with CaMRSA transmission and hygiene practices) will provide useful additional information.

Assess the need for additional studies

This may include an assessment of the environmental circumstances that could contribute to the outbreak (eg hand washing facilities and practices, towel sharing and washing) and further laboratory testing or screening of contacts.

Implement control measures

The case or relevant care-giver should be informed about the nature of the infection, the mode of transmission and the importance of hand washing and good hygiene for preventing infection. In addition to providing general hygiene information, PHUs should assess the need for providing support and access to further prevention measures in schools, sporting groups, and other high risk groups including:

• education of teachers, children and families about hand washing, and hygiene
• ensuring availability of hand washing products (soap dispensers, running water and disposable paper towel)
• ensuring that those with skin infections only use their own towel, clothes, and bed linen, and that no one else uses it
• structuring activities to allow time for hand washing (e.g. before eating and after going to the toilet)
• ensuring surfaces such as counters desks and toys are cleaned daily, or when ever visibly soiled, with detergent
• people who handle food must make sure that they don't contaminate any food and keep any sores or skin infections completely covered by a waterproof dressing
• consideration of temporary exclusion (from school, participation in contact sports, and shared spas or saunas) if open skin wounds cannot be kept covered or until wounds are healed or drainage can be contained. People who have open skin wounds should not share sports equipment that is in contact with the skin.
• community level education (e.g. how to avoid infection and what to do if infection occurs) may be warranted where widespread MRSA transmission occurs in a well-defined setting).

Bacterial decolonisation?

Current evidence does not support the routine use of agents to eliminate colonisation. However, it may be reasonable to try and eliminate staph carriage if:

• an individual has multiple documented recurrences of CaMRSA infection, or
• ongoing CaMRSA transmission occurs in a well-defined, closely-associated group (such as a household or sporting group)

Key points for a decolonisation procedure include:

• All household members with skin and soft tissue infections should be treated at the same time.
• Use an antiseptic wash or soap containing triclosan 1% or chlorhexidine 2% daily for bathing/showering for at least 5 days. If boils are occurring on the scalp, use a shampoo or soap containing an antiseptic.
• Regularly clean the household environment with a standard household detergent
• Discourage sharing of clothing, towels, or other linen that comes in contact with the skin.
• Sports/games that cause sweating and friction with clothes should be temporarily avoided.
• Use a topical nasal cream such as mupirocin 2% or chlorhexidine 0.3% nasal cream, applied intranasally with a cotton bud stick, three times daily for 10 days. The widespread use of mupirocin often causes resistance, and should be used after skin infections are controlled

Communicate findings

Document findings to convey recommendations about the immediate control of CaMRSA outbreaks and to provide evidence for policies designed to prevent future outbreaks.

Communicate findings back to those affected by the outbreak and relevant health care providers.

4. References

1. Gorwitz RJ, Jernigan DB, Powers JH, Jernigan JA, and Participants in the CDC Convened Experts' Meeting on Management of MRSA in the Community. Strategies for clinical management of MRSA in the community: Summary of an experts meeting convened by the Centers for Disease Control and Prevention. 2006.
2. Barton M, Hawkes M, Moore D, Conley J, Nicolle L & Upton A. etal. Guidelines for the prevention and management of community-associated methicillin-resistant Staphylococcus aureus: A perspective for Canadian health care practitioners. Canadian Journal Infectious Diseases Medical Microbiology 2006; 17 (Supp C).
3. Nathwani D, Morgan M, Masterton RG, Dryden M, Cookson BD, French G and Lewis D. Guidelines for UK practice for the diagnosis and management of methicillin-resistant Staphylococcus aureus (MRSA) infections presenting in the community. Journal of Antimicrobial Chemotherapy 2008; 61: 976-994.
4. Communicable Disease Control Directorate. Guidelines for the management of significant clones of MRSA in Western Australia Communicable Disease. WA Department of Health 2007.

5. Further information and resources

• NSW Health MRSA in the community - Information for the general public fact sheet.
• Therapeutic Guidelines Ltd. eTG complete (subscription required).