Group B streptococcus (clinical analyzes)



Group B streptococcus (GBS) is one of the many bacteria present in the body where it does not normally cause any kind of problem. The person who "hosts" the GBS without having disorders (symptoms) caused by its presence, is indicated with the term GBS carrier or colonized by GBS.

It has been estimated that about one in four women are pregnant carrier or colonized from GBS in the gastrointestinal and / or genitourinary tract.

Women carriers of GBS can have perfectly healthy babies. However, the presence of the bacterium in the woman during pregnancy is a risk factor for the newborn that could acquire the bacterium during the passage through the birth canal and, in a small percentage (1-2%), develop an invasive infection such as pneumonia. , meningitis, infections spread throughout the body (sepsis), death.

It is therefore important to carry out the test because, if the woman is colonized by GBS, it is possible to carry out prevention at the time of delivery to minimize the risk of the onset of neonatal infection. This consists of intravenous administration of ampicillin to the mother in labor.

The test

The examination (test) for group B streptococcus (GBS) should be performed between the 36th and 37th week of gestation. It consists in the collection of vaginal and rectal samples with a swab similar to a cotton swab (vagino-rectal swab ).The same swab can be used by first making the vaginal and then the rectal sampling or two different swabs. Cervical, perianal, perirectal, or perineal specimens are not acceptable specimen types. A speculum should not be used for specimen collection. Since the presence of GBS can be intermittent or transient, it is important that the samples are taken within the time interval indicated; if the test is performed more than 5 weeks before delivery, it is not very reliable.

The presence of GBS is verified by "culture analysis of the vagino-rectal swab. The broth enrichment of the sample (which consists in placing the swab in a liquid microbiological medium at 37 ° C for 18-24 hours) before" sowing "on a selective solid medium for the identification of the bacterium is a fundamental step for the reliability of the result." As indicated in the guidelines, enrichment minimizes the possibility of a false negative test result that would lead to the failure to administer intrapartum antibiotic prophylaxis thereby increasing the risk of developing invasive infection in the newborn. GBS research falls within the Essential Levels of Assistance (LEA) in the Official Gazette of March 18, 2017 - Supplement 15 (service code 91.08.4).


The result of the culture examination of the vagino-rectal swab provides important information to the gynecologist who, in the event of a positive test and ascertained risk conditions, will prescribe specific antibiotic prophylaxis during birth for the prevention of invasive neonatal group streptococcal disease. B (GBS).

If the vagino-rectal swab has not been performed, or has been performed outside the recommended period, antibiotic prophylaxis should still be performed in the presence of some risk conditions:

  • I leave before the term (gestational age less than 37th week)
  • fever in mom (> 38 ° C)
  • prolonged rupture of the membranes (> 18 hours)
  • previous child with neonatal infection
  • GBS urinary infection during pregnancy


Physiological pregnancy guidelines 2011

Centers for Disease Control and Prevention (CDC). Group B Strep (GBS) (English)

The American College of Obstetricians and Gynecologists (ACOG). Prevention of group B streptococcal early-onset disease in newborns. ACOG Committee Opinion No. 797 (English)

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