Streptococcal disease (Group A beta-haemolytic streptococcus)

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Streptococcal disease (Group A beta-haemolytic streptococcus)

Victorian statutory requirement

Notification is not required.

School exclusion: exclude until the child has received antibiotic treatment for at least 24 hours and the child feels well.

Infectious agent

Streptococcus pyogenes or Group A streptococci (GAS) has approximately 80 serologically distinct types. Those producing skin infections are usually of different serological types to those that cause throat infections.

Identification

Clinical features
The spectrum of disease caused by GAS includes:

superficial infections such as pharyngitis, impetigo and pyoderma
scarlet and puerperal fever
severe invasive disease such as necrotising fasciitis, toxic shock syndrome and septicaemia
post-streptococcal immunological sequelae include acute rheumatic fever and acute glomerulonephritis.

Method of diagnosis
Superficial infection is diagnosed by isolation of the organism from infected tissues. Invasive infection can be confirmed by isolation of the organism from a normally sterile site such as blood. Throat swabs are of limited value due to the frequency of inapparent Streptococcal carriage. Definitive identification depends on specific serogrouping procedures.

Antigen detection tests are available for rapid identification. A rise in serum antibody titres (anti-streptolysin O, anti-hyaluronidase, anti-DNAase B) may also be demonstrated in sera taken in the acute and convalescent phases of the disease.

Incubation period

The incubation period is usually one to three days.

Public health significance & occurrence

The incidence of GAS infections and their sequelae are not well documented in Australia except in Aboriginal communities in northern Australia. In the USA, acute pharyngitis is one of the most common reasons for seeking medical advice and GAS is thought to be responsible for 15–30% of pharyngitis in children and 5–10% in adults. The community burden of pyoderma in industrialised countries in not well documented.

Preliminary data from a voluntary surveillance system implemented in Victoria in 2002 suggests the incidence of invasive GAS disease may be greater than 4 per 100 000 per year, with a case-fatality rate of approximately 11%.

Outbreaks occur in childcare settings, institutions, and in remote communities in northern and central Australia.

Reservoir

Humans.

Mode of transmission

GAS is usually transmitted via large respiratory droplets or direct contact with infected persons or carriers. It is rarely transmitted by indirect contact through objects. Outbreaks of streptococcal infection may occur as a result of ingestion of contaminated foods such as milk, milk products and eggs.

Period of communicability

With appropriate antibiotic therapy GAS is communicable for 24–48 hours. In untreated uncomplicated cases communicability can last for 10–21 days. Communicability can be prolonged in untreated complicated cases.

Susceptibility & resistance

Pharyngitis and tonsillitis are common in children aged 5–15 years, whereas pyoderma occurs more frequently in children aged less than five years. Most people in their lifetime will develop a GAS throat or skin infection and many of the throat infections may be subclinical. People with chronic illnesses like cancer and diabetes, those on kidney dialysis, or those who use medications such as steroids, have a higher risk than healthy persons. There is an increased risk of infection in varicella (chickenpox).

Control measures

Preventive measures
There are currently no vaccines available but candidate vaccines are being used in clinical trials. Food-borne disease can be prevented by pasteurising milk and milk products and careful preparation and storage of high risk foods, particularly eggs.

Control of case
Treatment is dependent on the clinical presentation and severity of disease. Evidence has accumulated that antibiotics may not always be indicated in pharyngitis or tonsillitis. The current version of Therapeutic guidelines: antibiotics (Therapeutic Guidelines Limited) should be consulted prior to treatment.

Infected children should be excluded from schools and children’s services centres until they have received antibiotics for at least 24 hours and the child feels well. People with skin lesions should be excluded from food handling until infection has resolved.

Control of contacts
Consider the diagnosis in symptomatic contacts. Few people who come in contact with GAS will develop invasive GAS disease. At present, the role of antibiotic prophylaxis for close contacts of cases of invasive GAS infection is uncertain. However in certain circumstances, antibiotic therapy may be appropriate for those at higher risk of infection.

Control of environment
Standard infection control procedures should be applied.

Outbreak measures

Outbreak management is dependent on the setting and specific disease. Seek advice from the Department of Health.

Additional sources of information

Passmore, J, Kelpie, L & Carapetis, J 2003, ‘ Victorian Infectious Diseases Bulletin-June 2003’, Victorian Infectious Diseases Bulletin, vol. 6, no. 2, p. 30.

Infectious diseasesepidemiology and surveillance