Group A and B Streptococcus

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In France, invasive group A Streptococcus infections have been on the rise 2000

Around 500 cases of invasive neonatal group B Streptococcus infection are recorded each year in France

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Transmission and associated diseases

Group A Streptococcus

Group A Streptococcus (GAS), Streptococcus pyogenes, can only be spread through human-to-human transmission. It is responsible for frequent benign, non-invasive infections, such as strep throat and impetigo, as well as severe invasive infections such as bacteremia, necrotizing skin infections, puerperal infections, pleuropneumonia and meningitis, which may be associated with streptococcal toxic shock syndrome. The overall mortality rate from invasive GAS infections is thought to be approximately 10% (the respective mortality rates are 30% for streptococcal toxic shock, 15% for necrotizing dermohypodermitis and 20% for meningitis).

Group B Streptococcus

The main reservoir of group B Streptococcus (GBS), Streptococcus agalactiae, is the digestive tract, from where the bacteria may colonize the female genital tract, often on a sporadic basis. Between 5 and 40% of women are thought to carry GBS in their vagina during pregnancy, depending on the bacteriological techniques used and the populations under study. Neonatal infections are mostly linked with the inhalation and ingestion of vaginal secretions during childbirth. Mother-to-child transmission essentially occurs if the baby inhales or ingests infected amniotic fluid when the fetal membranes rupture or during delivery by passage through a GBS-colonized birth canal. The transmission rate from mothers with GBS to newborns is 50% on average, and approximately 1 to 2% of newborns go on to develop an infection if antibiotic prophylaxis is not administered to women with GBS colonization during childbirth.

 

GBS infections in newborns may be divided into two types, depending on when they occur: early-onset infections, 80% of which occur during the first 24 hours of the infant's life, and late-onset infections, which occur between the first week and the third month. Early-onset infections generally present with respiratory distress and bacteremia (in 89% of cases). Meningitis remains a less common clinical presentation in early-onset forms (10-20% of cases). Late-onset neonatal infections are associated with bacteremia and meningitis in most cases.

 

Clinical presentations in pregnant women vary, ranging from urinary tract infections to sepsis (generalized infection). Most invasive infections in pregnant women present as bacteremia, sometimes associated with intrauterine infections (infection of the placental tissue). Infection with group B Streptococcus outside the context of pregnancy and early infancy mainly gives rise to bacteremia, but cases of arthritis, endocarditis and meningitis have also been reported. Age and underlying medical conditions such as diabetes or cancer are risk factors.

Epidémiology

Group A Streptococcus

A number of epidemic phenomena received large-scale media coverage in the mid-1980s, especially an increase in acute rheumatoid arthritis in the United States and "flesh-eating" bacteria in the United Kingdom. Isolated cases of necrotizing dermohypodermitis and streptococcal toxic shock syndrome characterized by rapid progression and death highlighted the need to monitor S. pyogenes infections. These phenomena were observed in conjunction with a significant rise in invasive group A Streptococcus infections in industrialized countries, especially in Europe. In France, these invasive infections have been on the rise since 2000, with the incidence rate increasing from 1.2 to 3.3/100,000.

Group B Streptococcus

In France, around 500 cases of invasive neonatal infection are recorded each year, leading to between 30 and 60 deaths. The mortality of neonatal infections caused by GBS, although still high, has significantly decreased since the introduction of a screening test for pregnant women associated with prophylactic antibiotic treatment during childbirth in the event of vaginal colonization. Systematic screening and related prophylactic treatment have led to a considerable fall in the early-onset infection rate but have had little effect on the frequency of late-onset infections.

Treatment

Group A Streptococcus

Antibiotics known as ß-lactams are currently the treatment of choice for streptococcal infections. For several years now we have seen a rise in resistance to some classes of antibiotics, especially macrolide, lincosamide and streptogramin (MLS) antibiotics, which are often prescribed in pediatrics (children over the age of 3) or in adults, especially to treat ENT or respiratory tract infections or in the event of allergies to ß-lactams. Close contacts of patients with an invasive S. pyogenes infection are at greater risk of contracting a secondary infection than the rest of the community.

Group B Streptococcus

In pregnant women, systematic screening for S. agalactiae is recommended between 34 and 38 weeks of amenorrhea. Intrapartum antibiotic prophylaxis is based on a ß-lactam (penicillin or amoxicillin) or, in the event of an allergy, on a macrolide.

In newborns, treatment mainly involves the intravenous administration of a ß-lactam (amoxicillin), possibly in conjunction with another antibiotic (gentamicin) for the first 48 hours, over a period of 10 days to 3 weeks depending on the site of infection (meningitis, arthritis, etc.).

Vaccine

Group A Streptococcus

No vaccine currently exists for group A Streptococcus infections. Several vaccine candidates have been or are being developed, using different antigens and drawing on knowledge about the pathophysiological mechanisms of infection. The considerable genotypic and phenotypic diversity within the species greatly complicates the task of developing a vaccine covering all the strains responsible for infection.

Group B Streptococcus

There is currently no vaccine available for group B Streptococcus infections. Phase III trials with a trivalent conjugate vaccine based on capsular antigens are ongoing, as are trials in pregnant women with a hexavalent conjugate vaccine. These vaccines, developed by private laboratories, operate on a similar principle to commercially available vaccines targeting the pneumococcal (Streptococcus pneumoniae) capsule. Knowledge of the S. agalactiae genome (sequenced in 2002) has also opened up new avenues for vaccine development.

At the Institut Pasteur

The Biology of Gram-Positive Pathogens Unit, led by Patrick Trieu-Cuot, is conducting research on group B Streptococcus. The unit's research focuses on understanding the molecular mechanisms associated with virulence. It could lead to innovative technologies for diagnosing GBS infections and to the development of a new vaccine approach.


Mars 2021



Afaq iso 9001 - Institut Pasteur


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