Group B streptococcal infection

Overview

Streptococcus agalactiae, commonly known as Group B streptococcus (GBS), is a bacterium that is commonly found in diverse species including humans, mammalian animals, amphibians, reptiles and fishes.

GBS is commonly found in the gastrointestinal and genital tract of adults, without causing any disease. However, GBS may occasionally cause invasive infections of the blood, skin, joints, bone, heart, lungs and brain. GBS can also cause blood infection in infants if acquired from mothers during childbirth.

A specific strain of GBS, sequence Type 283 (ST283), has been associated with invasive disease in otherwise healthy adults or adults with relatively few underlying comorbidities.

Pathogen(s)

Group B Streptococcus (GBS) or Streptococcus agalactiae

Transmission

The bacteria are commonly found in gastrointestinal and genital tracts.

Vertical transmission (from mother to child):

• Occurs in pregnant women with GBS vaginal colonisation

• The highest risk occurs during late pregnancy (35-37 weeks gestation)

• Can affect foetus in utero or neonate during delivery

• Transmission rates of up to 50% without proper intrapartum antibiotic prophylaxis

While infections can spread within healthcare settings, such occurrences are relatively rare.

ST283 GBS is associated with the consumption of raw or undercooked freshwater fish or improper handling of freshwater fish.

Incubation period:

There is no defined incubation period for GBS acquisition to infection in adults. However onset of disease is usually within days.

For cases of mother-to-child transmission in neonatal infection, the incubation period is 1 to 6 days (early onset disease), and 7 to 90 days (late onset disease).

The average incubation period associated with consumption of raw freshwater fish is 3 to 5 days.

Infectious period:

In neonates (Newborns):

Mothers with GBS can transmit the bacteria during labour and delivery. They are considered potentially infectious at the time of childbirth.

In adults:

While symptomatic and if the bacteria are present in secretions or wounds. Risk of transmission in adults is generally considered low.

Clinical features

GBS can cause invasive disease. In adults, primary bacteraemia accounts for up to 20-50% of cases of first episode of infection.

Initial symptoms may be varied, including fever, chills, general malaise, drowsiness or altered mental status. The most common focal site of infection is the skin and soft tissues. Patients can present with cellulitis, abscesses, and less commonly, necrotising fasciitis. Other sites of GBS infection include urinary tract infection, septic arthritis, osteomyelitis, endocarditis and meningitis.

The common manifestations of neonatal infection are sepsis without a focal source, pneumonia, and meningitis.

Risk factors

• Infants born to mothers colonised with GBS

• Those aged 65 years and older

• Individuals with underlying medical conditions (e.g. diabetes mellitus, chronic liver, renal or pulmonary disease, malignancy, chronic alcoholism, immunosuppression, cardiovascular disease, cerebrovascular disease)

• Individuals who consume ready-to-eat raw or undercooked freshwater fish

• Individuals who handle freshwater fish and other aquatic products

Diagnosis

The presence of GBS infection can be confirmed by culturing samples from blood, cerebrospinal fluid or other sterile body fluids.

Treatment and Management

High doses of penicillin are usually needed to treat invasive disease. Occasionally, the addition of an aminoglycoside is required. Consultation with a doctor is recommended for the appropriate choice of antibiotics and duration. In patients with abscesses or necrotising fasciitis, adequate and timely surgical debridement is important.

Precaution, prevention and control

Intrapartum GBS prophylaxis should be considered for women colonised with GBS to reduce transmission and likelihood of neonatal infection.

To reduce the risk of foodborne GBS infection, good personal, food and environmental hygiene should be always maintained. These include:

• Proper food handling practices.

• Good hand hygiene after contact with aquatic products.

• Avoid consuming raw freshwater fish, and raw or undercooked aquatic products.

• Good wound care when wound is sustained during handling aquatic products; seek medical advice promptly when wound infection is found.

Resources

Singapore Food Agency - GBS and consumption of raw freshwater fish

National Centre for Infectious Diseases - Diseases and conditions