Infectious diseasesepidemiology and surveillance

Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance & occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control measures | Outbreak measures

Victorian statutory requirement

Notification is not required.

School exclusion: for impetigo due to staphylococcal infection exclude until appropriate treatment has commenced.

Infectious agent

There are nineteen species of staphylococci. The most significant human pathogens are Staphylococcus aureus and Staphylococcus epidermidis. Methicillin resistant S. aureus (MRSA) and vancomycin-resistant S. aureus (h-VISA, VISA and VRSA) are significant pathogens in hospital-acquired disease. Virulence varies greatly amongst the bacterial strains.

Identification

Clinical features
Staphylococcal infection presents with a variety of different clinical and epidemiological patterns amongst the general community, newborns, hospitalised patients and menstruating women. It may cause:

• purulent skin infections such as a boils, abscesses, styes, impetigo and scalded skin syndrome
• systemic infections such as pneumonia, osteomyelitis or endocarditis
• urinary tract infections due to S. saprophyticus in young women or S. epidermidis with indwelling catheters
• hospital-acquired (nosocomial) infection of surgical wounds or treatment lines
• food poisoning by releasing toxins into food
• toxic shock syndrome by releasing toxins into the blood stream.

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

Incubation period

The incubation period is variable and indefinite. It is most commonly four to ten days.

Public health significance & occurrence

Staphylococcal infections are frequent but are usually contained by immune mechanisms to the site of entry. Approximately 20–30% of the population are colonised with S. aureus in the anterior nasal passages. The highest incidence of disease usually occurs in people with poor personal hygiene, overcrowding and in children. However anyone can develop a serious staphylococcal infection including fit young people.

Since the late 1970s MRSA strains have been identified in Victoria as a major cause of nosocomial infections and outbreaks. MRSA accounts for approximately 30–50% of hospital-acquired S. aureus isolated from normally sterile sites. Vancomycin resistant strains have been reported. Health care employees and other carers may develop intermittent colonisation with MRSA. These workers rarely develop infection.

Reservoir

Human carriers are a major source of infection. Staphylococci have prolonged survival in the hospital environment due to resistance to antiseptics and disinfectants.

Mode of transmission

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

Period of communicability

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

Susceptibility & resistance

People who are most susceptible to infection are the chronically ill and newborns.

Mechanisms of immunity are not well understood. An experimental vaccine with a short duration of immunity has been developed to assist patients with end-stage renal disease.

Resistance to penicillin-related antibiotics in the hospital setting is common and includes MRSA. Two specific types of vancomycin antimicrobial resistant S. aureus called VISA and VRSA have recently emerged.

Control measures

Preventive measures
General measures:

• maintain good hygiene through public education in relation to hand washing, food preparation and avoiding sharing toilet articles
• cover purulent lesions with a waterproof dressing.

In the health care setting:

• educate hospital staff regarding the importance of hand washing
• use common narrow spectrum antibiotics where possible.

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

Control of contacts
Routine contact tracing is not usually required.

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

Control of environment
Encourage hand washing, especially in the hospital setting.

Outbreak measures

The Department of Health may investigate unusual clusters of staphylococcal infection in the community, particularly those associated with antibiotic resistant strains.

This may include:

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

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.

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.