Group B Beta Hemolytic Streptococcus

Introduction

Group B beta hemolytic streptococcus (or SBEGB) is involved in severe systemic and focal infections in the newborn, such as meningitis and pneumonia.

Just like group A beta hemolytic streptococcus, the protagonist of this article is also a component of the human bacterial flora. However, under favorable conditions, group B beta hemolytic streptococcus transforms from commensal to pathogenic opportunist, triggering a series of even serious infections in the host.
The progenitor of this serum group is known as Streptococcus agalactiae, responsible for meningitis and pneumonia (mainly), bacteremia and sepsis (less frequently) in infants and the elderly.
Group B beta hemolytic streptococcus has been (and still is) the subject of great interest, especially with regard to neonatal infections. In fact, it has been shown that an affected pregnant woman can transmit the bacterium to her child during childbirth: the risk of vertical transmission (mother-fetus) is very high.

Deepening

The beta hemolytic streptococcus of group B par excellence, the S. agalactiae, is a diplococcus classified according to its antigenic structure. The serological classification, established on the basis of the capsular polysaccharide and protein antigens, suggests distinguishing group B beta hemolytic streptococci in the following protein antigens: Ia, Ib, Ia / c, II, III, IV, V, VI, VII, VIII.
While the early forms of streptococcal infections (group B) can be induced by all the serum types just described, the late forms they are carried in almost all cases by type III.

Neonatal infections

Although it usually populates the normal gastrointestinal flora of many subjects, group B beta hemolytic streptococcus can spread to some secondary anatomical sites. It is estimated that the bacterium behaves as a commensal both in the male urethra and in the female genital mucosa (10-30% of cases): the transmission of the pathogen can occur through unprotected sexual intercourse.
As mentioned, the most serious problem is represented by the possible passage of the bacterium through the birth canal: in such circumstances, the newborn can face serious risks, such as septicemia, permanent damage and death.
The newborn is particularly susceptible to infections with S. agalactiae, since the cells of his immune system are not yet fully formed and / or efficient.

Risk factors

Some important risk factors that predispose a patient to group B beta hemolytic streptococcal infections have been identified:

Preterm infants (
Underweight babies
Rupture of the membranes for over 18 hours
Positive urine culture for S. agalactiae
Alteration of basal temperature during labor (> 38 ° C)
Cervicitis and vaginitis in the pregnant woman with consequent chorioamnionitis (infectious process affecting the amniotic cavity)
Previous child positive for beta hemolytic streptococcus type B

From recent statistical surveys, it appears that beta hemolytic streptococcus type B is present in one third of women of childbearing age and it is estimated that 1.8 children per 100,000 births are affected by streptococcal infections.

Symptoms

In the newborn, symptoms that distinguish group B beta hemolytic streptococcal infections tend to begin within the first week of life (early onset) or two to three months after birth (late onset):

Early onset of infection: Group B beta hemolytic streptococcus spreads through the blood, most commonly triggering septicemia associated with pneumonia (acute pulmonary syndrome)
Late onset of infection: The septicemic status caused by the streptococcal attack is most often accompanied by meningitis.

It should be emphasized that in both infectious forms (early and late) there is a high risk of spreading the pathogen to other anatomical sites (organs and tissues).
It is not uncommon for the newborn to complain of nonspecific symptoms: this constitutes a real obstacle for the diagnostic assessment. Not surprisingly, the main problem is precisely the manifestation of vague prodrome (fever, irritability, vomiting), which can delay the diagnosis, therefore postpone the start of a cure.
Late therapeutic intervention could cause serious permanent damage, especially neurological sequelae.

Diagnosis

The diagnosis is based on the identification of the etiopathological agent through culture examination. It is possible, even if less used, to search for the antigen with latex particles (also by urine culture). The most accredited diagnostic test seems to be PCR, highly sensitive and specific. CAMP-test is also a widely used diagnostic method for the identification of streptococci.

Therapy

Pregnant women who test positive for group B beta hemolytic streptococcus must undergo antibiotic prophylaxis during labor, which is essential to guarantee the unborn child "excellent protection from" infection.

Prevention

At present, there is no reliable preventive method to avoid the transmission of the bacterium to the newborn. However, if the test is positive for group B beta hemolytic streptococcus, preventive treatment with intravenous antibiotics (penicillin / aminoglycoside) before delivery is recommended.