Staphylococcal infections

Notification requirement for staphylococcal infections

Notification is not required.

Primary school and children’s services centres exclusion for staphylococcal infections

For impetigo due to staphylococcal infection, exclude until appropriate treatment has commenced.

Infectious agent of staphylococcal infections

There are more than 40 species of Staphylococcus. They are often commensal organisms of the skin and upper respiratory tract. Infection may result from endogenous organisms or may be transmitted from close contacts. It is important to differentiate coagulase-positive staphylococci, predominantly Staphylococcus aureus, from coagulase-negative staphylococci (for example, S. epidermidis). This is because of the greater virulence of S. aureus and the more significant role it plays in both community- and hospital-acquired infections. Resistance is a significant concern for both S. aureus and coagulase-negative staphylococci.

Identification of staphylococcal infections

Clinical features

Staphylococcal infection presents with a variety of clinical and epidemiological patterns among the general community, newborns, hospitalised patients, menstruating women and intravenous drug users.

S. aureus may cause:

• purulent skin infections such as boils, abscesses, styes, impetigo and scalded skin syndrome
• systemic infections such as bloodstream infections, pneumonia, osteomyelitis, endocarditis and deep abscesses
• hospital-acquired (nosocomial) infection of surgical wounds or treatment lines
• infections of prosthetic devices such as pacemakers, heart valves, joint replacements and other foreign bodies, including central venous catheters and peritoneal dialysis catheters
• food poisoning by releasing toxins into food
• toxic shock syndrome by releasing toxins into the bloodstream.

Coagulase-negative staphylococcal infections are more likely to be healthcare associated. They may cause:

• urinary tract infections due to S. saprophyticus in young women or S. epidermidis with indwelling catheters
• infections of prosthetic devices such as pacemakers, heart valves, joint replacements and other foreign bodies, including central venous catheters and peritoneal dialysis catheters
• similar infections to S. aureus in some circumstances (for example, immunosuppression), particularly the species S. lugdunensis.

Diagnosis

Diagnosis is confirmed by isolation of the organism from relevant specimens. The antibiotic resistance profile is important in management.

Incubation period of staphylococci

The incubation period is variable and indefinite. It is most commonly 4–10 days.

Public health significance and occurrence of staphylococcal infections

Staphylococcal infections are frequent but are usually contained by immune mechanisms at the site of entry. The highest incidence of disease usually occurs in people with poor personal hygiene, people subject to overcrowding and children. However, anyone can develop a serious staphylococcal infection, including fit young people.

Since the late 1970s, methicillin-resistant S. aureus (MRSA) strains have been identified in Victoria as a major cause of nosocomial infections and outbreaks. MRSA accounts for approximately 30–50 per cent of hospital-acquired S. aureus isolated from normally sterile sites. However, alcohol-based hand hygiene programs have been successfully associated with a reduction in the rates of nosocomial infections. Healthcare employees and other carers may develop intermittent colonisation with MRSA. These workers rarely develop infection.

Community-associated outbreaks have been reported among close contacts, including wrestlers, football players, prison inmates, people in day-care centres, people in military quarters, homeless people, intravenous drug users and men who have sex with men.

Reservoir for staphylococci

Human carriers are a major source of infection. Approximately 50 per cent of the population is colonised with S. aureus in the anterior nasal passages, some intermittently (~30 per cent) and some persistently (~20 per cent). This rate has declined over time; suggested reasons for this decline include improved personal hygiene, changes in socioeconomic class and smaller families.

Staphylococci have prolonged survival in the hospital environment due to resistance to antiseptics and disinfectants. Specific reservoirs, such as pigs, have been the source for outbreaks in humans who work directly with these animals.

Mode of transmission of staphylococci

Staphylococci are most often transmitted by direct or indirect contact with a person who has a discharging wound or clinical infection of the respiratory or urinary tract, or who is colonised with the organism. MRSA can be carried on the hands of healthcare personnel, and this is a likely mode of transmission between patients and staff. Contaminated surfaces and medical equipment are also possible sources of MRSA.

Period of communicability of staphylococcal infections

Communicability exists as long as purulent lesions continue to drain, or the carrier state persists.

Susceptibility and resistance to staphylococcal infections

Staphylococcal infection can affect people of any age, with or without comorbidities. Particular groups at higher risk include those who use intravenous drugs or have intravenous devices (for example, dialysis access lines, chemotherapy ports, long-term indwelling catheters), diabetics, burns patients, those who are immunosuppressed, the elderly and newborns.

Mechanisms of immunity are not well understood, although adequate neutrophil function plays a critical role.

Penicillin resistance was first described in 1944, and is currently present in more than 95 per cent of S. aureus isolates. Methicillin (as a marker of flucloxacillin) resistance was detected soon after the introduction of methicillin in 1959, and was first described in Australia in 1965. Approximately 25 per cent of S. aureus bacteraemia isolates were resistant to methicillin in a 2009 Australian study. MRSA are classified as hospital acquired (HA-MRSA; acquired >48 hours after admission to a hospital) or community acquired (CA-MRSA). Traditionally CA-MRSA isolates retained sensitivity to other anti-staphylococcal antibiotics (clindamycin, cotrimoxazole), whereas HA-MRSA were resistant to many classes of antibiotic, and most required intravenous vancomycin treatment. Vancomycin-resistant organisms are rare but concerning pathogens. They can be classified as VISA (vancomycin-intermediate S. aureus), h-VISA (heterogeneous vancomycin-intermediate S. aureus) or VRSA (vancomycin-resistant S. aureus). S. epidermidis is very frequently methicillin resistant (MRSE).

Flucloxacillin and first-generation cephalosporins (cephazolin, cephalothin) have been associated with the best outcomes for treatment of MRSA, and should be used in preference to other antibiotics. MRSA infections may or may not retain sensitivity to clindamycin or cotrimoxazole. Other antibiotics used for MRSA include vancomycin, rifampicin, fusidic acid, daptomycin and linezolid. Occasionally, for toxic shock syndrome or severe cellulitis, clindamycin is added to an anti-staphylococcal agent in an effort to minimise toxin production.

Control measures for staphylococcal infections

Preventive measures

General measures:

• Maintain good hygiene through public education in relation to handwashing, food preparation and avoiding sharing toilet articles.

• Cover purulent lesions with a waterproof dressing.

• In the healthcare setting

o educate hospital staff regarding the importance of handwashing

o use common, narrow-spectrum antibiotics, where possible

o consider decolonisation in patients planned for high-risk surgical procedures (see ‘Outbreak measures for staphylococcal infections’).

Control of case

Advise isolation until treatment of the infection has commenced. Search for, and cover, draining lesions. Infected people should avoid contact with infants and chronically ill patients. Added infection control precautions may be recommended for cases with infections due to multiresistant organisms.

Control of contacts

Routine contact tracing is not usually required.

Determining the carrier status of a pathogenic strain among family members may be occasionally useful. Carriers might be recommended antibiotics to eliminate the bacteria, such as mupirocin.

Control of environment

Encourage handwashing, especially in the hospital setting.

Outbreak measures for staphylococcal infections

The department may investigate unusual clusters of staphylococcal infections in the community, particularly those associated with antibiotic-resistant strains.

This may include:

• investigating the source of infection, including microbiological screening of contacts
• advising on added infection control precautions for cases and carriers
• making treatment recommendations for cases and carriers.

Within families or particular close-knit groups (sporting teams, prison inmates), treatment of carriers with a regimen to eliminate carriage of the bacteria may be recommended if a particularly virulent strain is causing issues with recurrent infection. Such ‘decolonisation’ involves the repetitive use of antiseptic body wash, in conjunction with intranasal antibiotics such as mupirocin.

Special settings

Hospital nursery workers with minor lesions, such as boils or abscesses, should not have direct contact with infants until the lesion has healed.

All known or suspected cases in a nursery should be isolated. Two or more concurrent cases would constitute an outbreak and warrant investigation. Identification and treatment of carriers may be necessary in this situation.

In school settings, the child should be excluded from school until specific treatment begins. Lesions must be covered with a watertight dressing. Contacts do not need to be excluded.