Would sensitive ‘gold standard’ (ECM) tests for detecting group B Strep carriage be helpful?
From April of 2014 through January of this year, we conducted a seven question survey (via Survey Monkey) asking both qualified and student midwives about testing for group B Strep carriage in pregnancy. The results are encouraging since at the heart of the survey more than 80% said testing should be available through the NHS AND that they would use it!
Following on from the revelations of the RCOG audit1 last month, health professionals are recognising that the RCOG’s guidelines are failing. Many maternity units are eager to reduce the number of group B Strep infections on their watch, but the right tools and information are not being made available to them. In addition to the breakdown of the questions below, there were several ‘Additional Comments’ we were keen to respond to. For the purpose of this blog, we are looking at the percentages in favour.
1.In the last 12 months, has a pregnant woman asked you to test her for group B Strep carriage?
a. (Midwives) 40.1% = Yes
i.(Student Midwives) 32%
2.In the last 12 months, have you requested a test for a pregnant woman specifically to check for GBS carriage?
a.Yes, requesting an NHS test for GBS carriage = 30.7%
i.24.24%
b. No, though I suggested she request a private test for GBS carriage = 16%
i.21.21%
3.Currently, in the UK, the 'gold standard' enriched culture medium test for detecting group B Strep carriage (UK SMI B58)2 is not widely available within the NHS. Do you think that this test should be available?
a. 82.5% = Yes
i.77.1%
4.Are there situations in which you would want to test a pregnant woman for GBS carriage using the 'gold standard' test (UK SMI B58)?
a. 85.4% = Yes
i.82.3%
5.In what situations would you want to test a pregnant woman for GBS carriage using the 'gold standard' test (UK SMI B58)? Where she… (tick all that apply)
a.has previously had a baby who developed invasive GBS infection = 76.9%
b.has pre-labour rupture of membranes = 66.5%
c.carried GBS before the current pregnancy = 61.8%
d.is in threatened preterm labour = 59%
e.carried GBS earlier in the current pregnancy =58.5%
f.wants to establish her GBS carriage status = 53.8%
g.Other =10.4%
*The above percentages are the combined responses of both qualified and student midwives
6.Do you think ALL pregnant women should be offered testing for group B Strep carriage using 'gold standard' methods as a routine part of their antenatal care?
a.65.1% = Yes
i.53.2%
7.Additional Comments: There were 45 additional comments, many of which overlapped and repeated. We chose the following as they hit all the necessary bullet points in the on-going group B Strep conversation.
“I don’t know what the benefits of the gold standard test are compared to the usual test.”
1.The conventional NHS test (Standard Direct Plating): This is the method generally used in the NHS when a swab is taken to investigate vaginal symptoms. It was not specifically designed to detect group B Strep and is not a sensitive test for this purpose. Usually only a vaginal (and often a high vaginal) swab is taken. In the lab, the cells from the swab are transferred onto a dish or ‘plate’ containing agar (a non-enriched growth medium) and after 24 and 48 hours incubation, the plate is examined to see if GBS has grown.
a.A positive result using this test method is highly reliable – there are few falsely positive results.
b.A negative result using this method is not very reliable – it gives a high proportion of falsely negative results. GBS will be isolated in only around 50% of cases where the Mum is carrying GBS as the swab was taken.
2.The ECM test (Enriched Culture Method): Designed specifically to detect group B Strep carriage, this ‘gold standard’ test is described by Public Health England’s UK SMI B583. It is available from a small but growing number of NHS trusts and a number of private labs (some of which offer postal or at-home-testing services). Samples are taken from the low vagina and rectum (either one combined vaginal/rectal swab or two separate swabs processed as one) which are then sent off to the laboratory specifically marked “for GBS culture in ECM”. The cells from the swab(s) are incubated in an enriched culture medium specifically designed to encourage the growth of GBS and thus enhancing its detection. Research has shown that, when the ECM test is properly performed within 5 weeks of delivery (35-37weeks):
a.A positive result was 87% predictive of carrying GBS at delivery (13% of women lost carriage between performing the test and giving birth)
b.A negative result was 96% predictive of not carrying GBS at delivery (4% of women acquired carriage between the test and giving birth) 4
"Transient colonisation. Only screens and protects (with prophylaxis) early onset GBS infection. Too much use of antibiotics resulting in superbugs, etc."
Group B Strep carriage can come and go from the vagina quite naturally over a period of time, but this isn’t a daily or even weekly occurrence. The result of a sensitive test for GBS carriage (ECM) is highly predictive for the following 5 weeks. So testing at 35-37 weeks of pregnancy is very good at predicting whether a woman will be carrying when she is most likely to go into labour – during the next 5 weeks.
Intrapartum antibiotic prophylaxis (IAP) can only protects against early-onset GBS infection (0-6 days of life), which accounts for up to 3 out of 4 group B Strep infections in babies. If Mum knows she was carrying group B Strep around the time of delivery then she can be educate herself on the signs and symptoms of late-onset GBS infection to watch for. Late onset can occur from 7 days to 3months of life and is not currently preventable. However, recognising the symptoms and taking the baby for early and appropriate treatment is vital in improving the outcome for babies with late onset group B Strep infection.
When women are given antibiotics in labour on the basis of known risk factors, instead of ECM test results, 71% will not actually be carriers of group B Strep. So almost three quarters of women are already being given antibiotics to prevent EOGBS infection unnecessarily!
“The NHS is strapped for cash as it is and routine testing would just encourage unnecessary interventions and worry. Testing based on clinical indication is sufficient.”
Public Health England report the cost of the Enriched Culture Medium test to the NHS as £11. UK research has shown that the health and social care costs for babies with group B Strep infection is, on average, DOUBLED during their first two years compared with those without it.5
Knowing whether a mum is a GBS carrier allows her to make an informed decision for herself and her unborn baby. Routine testing would not mean she is forced to have antibiotics in labour. She would merely be offered the option based on known group B Strep carriage. Offering antibiotics in labour based on clinical indication is NOT a good predictor of which newborn babies are most at risk of developing group B Strep infection since up to 40% of babies who do are born to mothers without any of these clinical indications. The current risk-based prevention strategy has failed to reduce the rate of group B Strep infections since it was introduced in 2003.
“No evidence to support routine testing”
Studies have repeatedly shown that countries that DO offer routine antenatal screening for group B Strep carriage and antibiotics in labour to Mums carrying group B Strep have seen the rate of group B Strep infections fall significantly - by 71-86% in France, USA, Spain and Australia 6-9
Very recently in the UK, Northwick Park Hospital has introduced universal antenatal screening for group B Strep in response to the trust’s very high incidence of group B Strep infection in newborn babies. In the programme’s first 12 months, they have seen no cases of early onset group B Strep infection in babies born to women who were screened. A poster presentation at the 2015 BMFMS10 reported how well the programme has been received among pregnant women and data from this study are to be published later in 2015.
“Concerned that false negative results may give rise to complacency.”
Yes, exactly. This is why any tests for group B Strep carriage need to use a method which is sensitive at detecting the bacteria. It should follow the standard published by Public Health England on the Enriched Culture Medium test - NOT the standard NHS test. The standard NHS swab produces a high proportion of false negatives – not surprisingly as it was not designed specifically to find group B Strep bacteria – and misses up to 50% of all GBS carriers at the time the swab was taken. These standard-test results can give a false sense of security or ‘complacency’.
“Given that such a high proportion of women carry GBS without incident, testing everyone and potentially treating everyone with IV antibiotics would cause more deaths from anaphylactic shock--nevermind future antibiotic resistance--than would be saved from GBS, tragic though these deaths are.”
Yes, most women who are group B Strep carriers go on to have healthy babies with no incident. The risk of baby developing an early-onset GBS infection when born to a woman carrying group B Strep late is one in 300 when no preventative measures are taken. Testing every pregnant woman does not automatically mean every pregnant woman will receive (or want) IAP. Only the women who test positive for GBS carriage should be offered antibiotics in labour, and those with other recognised risk factors.
Approximately 10% of babies with group B Strep infection die, so approximately:
•1 in 3,000 babies born to women carrying group B Strep and where no preventative antibiotics are given die.
The generally quoted estimated risks for penicillin are:
•1 in 10 of the mother developing a mild allergic reaction, such as a rash;
•1 in 10,000 of the mother developing a severe allergic reaction (anaphylaxis); and
•1 in 100,000* of the mother developing fatal anaphylaxis, resulting in her death.
Research has shown that narrow spectrum intravenous antibiotics (ideally penicillin), given in labour to women whose babies are at higher risk of developing GBS infection, is highly effective at reducing the risk of GBS infection in newborn babies, without any known long-term side-effects on the baby. Indeed, GBS has remained sensitive to penicillin for over 60 years.
“I believe that women should be given the information about the risks and their options if it comes back positive. However for testing to be 'a routine part of their antenatal care negates the woman's autonomy as the consequences of the test ultimately means that her place of delivery choice is dramatically impacted.”
We believe that information and testing for group B Strep carriage should be offered as a routine part of antenatal care and that pregnant women should be encouraged to make an informed decision about what’s best for them and their babies.
Increasingly, intravenous antibiotics in labour are given outside as well as within consultant-led maternity units. Many alongside midwife led units will give women intravenous antibiotics in labour against group B Strep infection in their newborn babies, although many stand-alone units will not. Likewise, many home birth midwives are not able to give intravenous antibiotics in labour. Some areas won’t permit intravenous antibiotics to be given at home so a discussion will be needed.
As with other tests, pregnant women need to consider what action to be taken, if any, at each step. Not all will want to be tested. Not all who test positive will want antibiotics in labour – surely this needs to be their decision, made in conjunction with their health professionals and based on what is important to them and what is available locally?
“Sadly GBS is a terrible thing when it happens. More midwives looking after women, women being informed about their choices and not the reactive fear, loss of birth choices and medical intervention that is just not needed. Sorry I can not and do not support your cause.”
Women being informed about their choices IS our cause! We provide lots of information on testing and antibiotics to educate parents-to-be about all possible options. Yes, we would like to see the UK routinely offer the sensitive ECM test to all pregnant women between 35-37 weeks. But as importantly, we want mums to be aware of and educated about group B Strep so they can make the decision that is right for them and their babies.
For more information on group B Strep, please visit our website. If you want more about GBS research and/or the current UK guidelines in preventing early-onset GBS infection then visit our Professionals page.
All of our information leaflets, posters, and GBS Alert stickers are available for free. They can be downloaded or an ordered through our online shop.
References:
1 2015 RCOG audit of current practice in preventing group B Strep infection in newborns
gbss.org.uk/wp-content/uplo...
2 Public Health England’s UK Standards for Microbiology Investigations B 58 Processing Swabs for Group B Streptococcal Carriage (issued 2006, updated 2014, currently under review) – testing specifically for group B Strep carriage gov.uk/government/publicati...
3Albouy-Llaty M, Nadeau C, Descombes E, Pierre F, Migeot V. Improving perinatal Group B streptococcus screening with process indicators. J Eval Clin Pract 2011
4 The accuracy of late antenatal screening cultures in predicting genital group B streptococcal colonization at delivery. Yancey MK, Schuchat A, Brown LK, Ventura VL, Markenson GR. Obstet Gynecol. 1996 Nov;88(5):811-5. Am J Obstet Gynecol. 1984 Apr 1;148(7):915-28.
5 Schroeder EA, Petrou S, Balfour G, Edamma O, Heath PT. The economic costs of Group B Streptococcus (GBS) disease: prospective cohort study of infants with GBS disease in England. Eur J Health Econ. 2009 Jul;10(3):275-85. Epub 2008 Nov 11.
6 Jordan HT, Farley MM, Craig A, Mohle-Boetani J, Harrison LH, Petit S et al. Revisiting the need for vaccine prevention of late-onset neonatal group B streptococcal disease: a multistate, population-based analysis. Pediatr Infect Dis J 2008; 27(12):1057–1064.
7 Andreu A, Sanfeliu I, Vinas L, Barranco M, Bosch J, Dopico E et al. [Decreasing incidence of perinatal group B streptococcal disease (Barcelona 1994-2002). Relation with hospital prevention policies]. Enferm Infecc Microbiol Clin 2003;21(4):174–179.
8 Daley AJ, Isaacs D. Ten-year study on the effect of intrapartum antibiotic prophylaxis on early onset group B streptococcal and Escherichia coli neonatal sepsis in Australasia. Pediatr Infect Dis J 2004; 23(7):630–634.
9 Albouy-Llaty M, Nadeau C, Descombes E, Pierre F, Migeot V. Improving perinatal Group B streptococcus screening with process indicators. J Eval Clin Pract 2011.
10 Maternal experience of newly introduced antenatal group B Strep screening in a UK hospital. McQuaid F et al. BJOG Abstracts of the BMFMS 17th Annual Conference 2015. Vol 122. S2. PM51. P36. onlinelibrary.wiley.com/doi...
