Staphylococcus aureus bloodstream infection (SABSI) contributes to significant morbidity and mortality, with about 25 to 30% of hospital-acquired cases resulting in serious or life-threatening illness. Despite this, healthcare-associated SABSI is preventable (ACSQHC 2021; WA DoH 2017).
What is Staphylococcus Aureus?
Staphylococcus aureus bacteria (also known as S. aureus, golden staph or staph) is carried by approximately 20% of the population at any given time, with about 60% of people being colonised off and on during their lifetime (SA Health 2020).
S. aureus commonly inhabits the inside of the nose as well as the skin, where it is usually harmless and unnoticeable. However, if the bacteria is able to enter the body it may multiply and cause an infection (AIHW 2020; QLD DoH 2017).
Infection may be caused by bacteria from the patient’s own body, or via the transmission of bacteria from another person (VIC DoH 2015).
There are over 40 known species of S. aureus (VIC DoH 2015).
Types of Staphylococcus Aureus Infections
S. aureus infections range from mild to severe and may be life-threatening in some cases (Mayo Clinic 2020).
In some cases, S. aureus can colonise food, leading to food poisoning (Healthdirect 2020a).
Most S. aureus infections affect the skin (Healthdirect 2020a). These infections, known as staph skin infections, are often transmitted through skin-to-skin contact, touching contaminated objects or sharing items such as clothes and towels (QLD DoH 2017).
Staph skin infections include boils and abscesses, staphylococcal scalded skin syndrome (SSSS), impetigo, cellulitis and wound infections (Healthdirect 2020b; Better Health Channel 2015).
SABSI is associated with complications such as prolonged hospital stays, admission to critical care services, increased healthcare costs and even death in the most serious cases (AIHW 2019).
How Does a SABSI Occur?
In healthcare settings, most cases of SABSI are related to poor hand hygiene among staff, invasive devices and healthcare procedures (ACSQHC 2021).
S. aureus may be transmitted via contact with patients who have discharging wounds or infections or are colonised with the bacteria. If a staff member’s hands become contaminated with S. aureus, the bacteria may then be able to enter the bloodstream through open wounds, incisions or invasive devices (AIHW 2020; VIC DoH 2015).
Someone who becomes colonised with S. aureus will not necessarily develop an infection, but if they do, this could occur from days to years after the initial exposure. However, even if someone is asymptomatic, they are infectious as long as S. aureus is being carried on their skin (SA Health 2020).
A SABSI is considered to be healthcare-associated (HA-SABSI) if either:
An initial positive blood culture is taken more than 48 hours after admission or within 48 hours before discharge, OR
An initial positive blood culture is taken 48 hours or less after admission, AND:
The infection is the result of an invasive device complication, or
The infection occurred within 30 days of a surgical procedure and is related to the surgical site, or
The infection was diagnosed within 48 hours of an invasive instrumentation or incision that is related to the infection, or
The infection is related to neutropenia (less then 1 x 109/L) contributed to by cytotoxic therapy.
If the infection does not meet these criteria, it is considered to be community-acquired (ACSQHC 2016).
Over time, several strains of S. aureus have developed antibiotic resistance to certain medicines including penicillin, methicillin and vancomycin (Better Health Channel 2015). These strains, known as methicillin-resistant Staphylococcus aureus (MRSA), are difficult to treat as only a few types of antibiotics will work effectively (SA Health 2019).
For this reason, MRSA strains are associated with poorer patient outcomes (AIHW 2019).
MRSA strains are not only confined to hospital and healthcare settings and can also be community-acquired (CA-MRSA) (Healthy WA 2020).
Risk Factors for SABSI
A weakened immune system (due to cancer or a transplant)
Age (being very young or an older adult)
Chronic illness (e.g. diabetes)
Severe underlying illness
Having an invasive medical device in-situ (e.g catheter)
Prolonged antibiotic use
Sharing personal items (e.g. towels, razors)
Stays in healthcare settings (e.g. hospitals, residential aged care)
Use of injection medicines (e.g. opioids)
Outpatient surgeries and procedures (e.g. dialysis).
(Healthdirect 2020a; CDC 2019)
SABSI is generally treated with intravenous antibiotics upon diagnosis (SA Health 2019).
About 82% of SABSIs can be treated with commonly-used antibiotics (AIHW 2020).
Effective hygiene measures are essential in preventing the transmission of S. aureus and other healthcare-associated infections(AIHW 2019). Healthcare workers should ensure that they:
Follow hand hygiene practices, especially after touching wounds or wound dressings
Antibiotics must be used responsibly in order to reduce the risk of new resistant strains of S. aureus. Ensure that common, narrow-spectrum antibiotics are prescribed whenever possible (Better Health Channel 2015; VIC DoH 2015).
Other ways to prevent the spread of S. aureus include:
Ensuring patients’ wounds are appropriately covered in order to prevent S. aureus from entering the bloodstream
Ensuring patients’ staph skin infections (e.g. boils and infected wounds) are appropriately covered to prevent exposure to pus or drainage
Immediately disposing of used wound dressings in a sealed plastic bag
Washing the clothes, towels and sheets of an infected patient with detergent and hot water, then drying them in sunlight or using the hot setting of a clothes dryer
Ensuring that personal items (e.g. towels, razors) are not shared between patients
Taking additional precautions when treating patients with an MRSA strain (e.g. allocating them a single room with ensuite facilities).
(Better Health Channel 2015; SA Health 2020)
Surveillance refers to the monitoring and reporting of healthcare-associated infections in order to identify possible risk prevention strategies (VICNISS 2021; ACSQHC 2019).
In Australia, all cases of SABSI in acute public hospitals must be monitored and reported by their relevant jurisdictions to the National Health Care Agreements reporting system (ACSQHC 2016).
When testing for SABSI, two sets of blood cultures should be taken from two different body sites. If these results don’t match, further investigation is required as false positives of S. aureus only occur rarely (ACSQHC 2016).
When a SABSI case is identified, an assessment should occur in order to determine whether the case meets the definition of a healthcare-acquired infection (see above) (ACSQHC 2016).
The data collected through surveillance is used to identify preventable risk factors for SABSI, inform antimicrobial stewardship and develop strategies to improve patient safety (ACSQHC 2021).