Staph wound infections and MRSA

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Last Review Date: April 10, 2020

What are staph wound infections?

Staphylococcus aureus, also called S. aureus or staph, is a bacterium that commonly colonises the human skin and is present in the nose of about 25 to 30 per cent of adults. S. aureus can exist in this form without harming its host or causing symptoms. However, if there is a break in the skin from a wound or surgery or intravenous access device, or if there is a suppression of a person's immune system, colonising S. aureus can cause an infection.

Staph often causes localised skin infections such as infected hair follicles or boils (folliculitisfuruncles), and impetigo. It can also cause abscesses and spread into the bones (osteomyelitis), lungs (staphylococcal pneumonia), blood (bacteraemia or sepsis), heart (endocarditis) and other organs. Staph may also infect other people as it can be passed from both infected and colonised people to others through skin contact or through sharing contaminated objects, such as towels or razors.

Hospital-acquired infections

Hospital and healthcare acquired staph infections have been a challenge for many years. The confined population in hospitals and long-term care facilities combined with the widespread use of antibiotics have led to the development and spread of antibiotic-resistant strains of S. aureus. Staph organisms that are resistant to the beta-lactam antibiotics are called methicillin resistant Staphylococcus aureus (MRSA), named after the antibiotic treatment that was developed in 1960 to treat penicillin-resistant strains. Infections caused by MRSA are often resistant to a wide variety of antibiotics (multi-resistant) and are associated with significantly higher rates of complications and death (morbidity and mortality), higher health care costs, and longer hospital stays than infections caused by methicillin susceptible S. aureus.

Classic risk factors for MRSA infection in the hospital include surgery, prior antibiotic therapy, intensive care admission, exposure to a MRSA-infected patient or health care worker, being in the hospital more than 48 hours, or having an indwelling catheter or other medical device that puctures the skin. 

Community-acquired infections

MRSA infections in the community are becoming increasingly important, particularly over the past decade. They have been associated with a growing number of outbreaks and deaths in non-medical settings where individuals are in close contact, such as in contact sports, daycare facilities, military units and prisons. These infections are occurring in people who do not have any of the classic MRSA risk factors. Until recently, part of the problem with community-acquired MRSA (CA-MRSA) has been a lack of awareness, both in the medical community and the general population. Historically, doctors have treated staph infections with a standard course of antibiotics. They did not routinely order cultures to identify the microorganism and its antibiotic susceptibility profile unless the infection appeared extensive or the initial treatment was unsuccessful. When treating CA-MRSA, conventional therapies have often failed. A number of those affected have required hospitalisation for intravenous antibiotics and a few previously healthy people have died.

Investigations of these outbreaks have revealed that the CA-MRSA was spread from infected or colonised people to those around them through skin contact (such as sports-related cuts and abrasions), respiratory droplets (sneezing or coughing), or through exposure to contaminated objects (such as shared sports equipment, towels, toys, or playground equipment). Investigations also revealed that the S. aureus strains involved in CA-MRSA are not the same strains as those that are causing hospital-acquired MRSA; they are genetically distinct. The CA-MRSA are resistant to methicillin and related antibiotics (dicloxacillin, flucloxacillin, cefalexin) but often remain susceptible to many other antibiotics (non-multiresistant).  

Signs and Symptoms

Hospital-acquired MRSA

In the hospital, MRSA can cause very serious infections that spread to vital parts of the body. Depending on the location of the infection, it can cause signs and symptoms associated with:

  • Pneumonia - coughing, wheezing, difficulty breathing
  • Blood infection (bacteraemia) - fever, chills, rapid breathing
  • Infection of surgical sites or intravenous access sites - redness, swelling and pain
Community-acquired MRSA

In the community, MRSA infections most commonly affect the skin. They often appear:

  • Initially as small red bumps that look like pimples or spider bites
  • As red, swollen, painful pustules with draining fluid or pus
  • In areas with cuts or abrasions of the skin
  • In areas of the skin with hair, such as the back of the neck, groin or armpit

Laboratory Tests

The purpose of laboratory testing is to identify the bacteria causing the wound infection and to determine the susceptibility of the microorganism to available antibiotics. If an infection is due to MRSA, it should be investigated to determine the source of the infection.

Testing for staph infections:

  • The primary test for diagnosis of a staph infection is a culture of the affected area. This may involve a bacterial wound culture using fluid or pus from a wound, a sputum cultureblood culture, a culture of joint fluid (synovial fluid) or even breast milk (in the case of an infected breast). Sometimes, multiple samples are collected to evaluate different body sites or to attempt to detect bacteria that may be present in small numbers.
  • Susceptibility testing is performed if S. aureus are detected in a culture, to determine if the strain that is present is MRSA.

Rapid tests for the detection of MRSA have recently been developed. These tests are molecular-based or use immunoassay to determine if the drug-resistant bacteria are present. Whereas cultures typically take 24-48 hours, these tests provide results in 2-5 hours allowing for prompt action such as addition of different antibiotics and consideration of patient isolation in a hospital setting.

Identifying MRSA can sometimes be challenging. Most people have a mixed staph population. This means that even if someone has MRSA, not all of the staph present at the infection site will be equally resistant and  there is the potential for missing them.

A variety of methods can be used to track different strains of MRSA. These are used in the epidemiological investigation of the spread of MRSA within a community or region but are not used in the treatment of an individual person.

Prevention and Treatment

Hospital-acquired infections

Hospitals have had infection control measures in place for many years. Additional strategies that have been proposed in an effort to prevent and control the spread of MRSA infections include active surveillance – screening for the detection of MRSA infection or colonisation in those admitted to intensive care units (ICUs) and other high risk areas, screening all people admitted to a health care facility, and/or periodically screening health care workers.

MRSA screening:

  • A swab of the inside of the nose may be used to screen healthy people to determine whether someone has been colonised with MRSA and is a carrier. MRSA can be detected from the swab by carrying out a culture to see if MRSA grows or by a rapid molecular test. Molecular testing does not grow the bacteria but detects their presence and antibiotic resistance by identifying the genes responsible for the methicillin resistance.

People with serious invasive MRSA infections, such as sepsis, are often treated with vancomycin. This is an antibiotic that must be administered intravenously (IV), often for several weeks. In most cases, vancomycin will help to eliminate the MRSA infection but it does not prevent/eradicate colonisation. There are increasing reports of infections that do not respond to vancomycin therapy with vancomycin-resistant S. aureus (VRSA), vancomycin-intermediate S. aureus (VISA) and vancomycin heteroresistant S. aureus (hVISA). There are a limited number of alternative antibiotics available to treat infections caused by the MRSA that are less susceptible to vancomycin. There is growing concern in the medical community that we will eventually run out of treatment options for antibiotic-resistant S. aureus.

Community-acquired infections

Preventive measures are the mainstay of infection control in the community. This includes wound management (covering and antibiotics where required) and hygiene measures (frequent hand washing and/or the use of alcohol-based hand gels). For more on the most effective way to wash your hands, visit the Better Health (Victorian Government) web site.

Many sports teams and institutions have put procedures in place to more rapidly recognise and address MRSA infections. Health care providers are being urged to order cultures and susceptibility testing routinely with outpatient skin and wound infections, to monitor the affected person carefully for effectiveness of treatment, and to be alert for the possibility of CA-MRSA.

Related Pages

On this site
Tests: MRSA ScreeningBlood CultureGram StainVancomycinBacterial Wound CultureSynovial Fluid Analysis
Conditions: Septic ArthritisWound and Skin InfectionsPneumonia (LTO US), Sepsis

Elsewhere on the web

CDC: FAQs about MRSA (.pdf USA)
CDC: Vancomycin-Intermediate/Resistant Staphylococcus (VISA/VRSA) in Healthcare Settings (USA)

Staphylococcus aureus – golden staph (Victorian Health)
Australia faces big MRSA problem (Medical Journal of Australia - InSite)
MRSA in the community: information for the public (NSW health)