Pharmacy strep B testing: Noble cause, or an own goal for the profession?

: Dr Joseph Bush

: Ross Ferguson

WHAT more compelling reason could there be for introducing a pharmacy service than saving babies’ lives?

But, as scientists we need to consider the evidence of introducing such services instead of just doing what on the face of it may seem logical and the right thing to do.

Some pharmacies have started to deliver a Strep B testing service for women who are pregnant¹. The reason is that during labour babies can come into contact with Group B Streptococcus (GBS)², which occurs naturally in both men and women and is usually harmless². However, rarely it can result in infection in newborns.

If a baby develops GBS infection less than seven days after birth, it’s known as early-onset GBS infection³ — most babies who do become infected develop symptoms within 24 hours of birth (90% of cases)⁴.

The incidence of GBS in the UK is estimated to be 1 in 2,000 live births, which equates to 350–400 cases per year with a mortality rate between 5–10%, resulting in 25–40 neonatal deaths⁴.

There is a lack of evidence on morbidity due to GBS, but meningitis, sepsis and pneumonia and long-term complications such as cerebral palsy, deafness, blindness and learning difficulties have been reported in a minority of infected babies⁴.

Given the potentially dire consequences outlined so far, it appears superficially logical to screen expectant mothers for GBS. Let’s screen as many women as we can to save babies’ lives, and help prevent possible complications. What a worthy cause.

But, it’s important to note that most pregnant women who carry GBS have healthy babies, and that, where GBS is transmitted to a baby, the majority of the 0.05% of babies affected make a full recovery with prompt treatment⁵.

There is no argument that the anguish caused by the death of a child is indescribable for the families involved, and that one baby dying from this infection is one baby too many. But, like any clinical intervention, a decision to employ the intervention needs to be based on the balance of risks and benefits.

The NHS view
The NHS does not offer routine screening of women who are pregnant for Strep B infection, while it is offered in some other countries including the US⁴.

In the UK healthcare professionals are encouraged to identify and manage high risk pregnancies after assessment of the risk factors³.

So, why is that?

Well, following a comprehensive review of the evidence, the NHS independent expert screening committee has confirmed its recommendation that there should not be a national screening programme for GBS in pregnancy⁶.

The Royal College of Obstetrics and Gynaecology has warned against extrapolation of the US practice of the systematic screening of pregnant women to the UK. This is because, even though pregnant women in the US are routinely screened, whereas those in the UK are not, the incidence of GBS disease in the UK is similar to that in the USA even though both countries have comparable vaginal carriage rates⁷.

Moreover, while intrapartum antibiotic prophylaxis (IAP) has been shown to significantly reduce the risk of early-onset GBS, it has not been shown to have the same effect on late-onset disease (occurring 7 or more days after birth)⁷.

Also, a Cochrane review concluded that, while the use of IAP in colonised mothers reduced the incidence of GBS disease, it did not reduce all-cause mortality or GBS-related mortality⁸.

Test limitations
It has been suggested that offering screening at 35 to 37 weeks of pregnancy will help detect women carrying GBS who are more at risk of passing on the bacteria during labour⁶. However, the UK National Screening Committee (UK NSC) found that even screening at this later stage would potentially expose people to unnecessary harms, with large numbers of people receiving antibiotics unnecessarily⁶.

At the launch of the latest review, Dr Anne Mackie, Director of Programmes for the UK NSC, said:

“At the moment there is no test that can distinguish between women whose babies would be affected by GBS at birth and those who would not. This means that screening for GBS in pregnancy would lead to many thousands of women receiving antibiotics in labour when there is no benefit for them or their babies and the harms this may cause are unknown.

“This approach also cuts against the grain of ongoing efforts to reduce the number of people receiving unnecessary antibiotics. Much better evidence is needed on such widespread antibiotic use among pregnant women and whether it is possible to find a more accurate test.”

And while the UKNSC says there was evidence that the introduction of antenatal GBS screening for all pregnant women may lower the number of babies with GBS, it says these studies have limitations, which means their findings might not automatically translate to real world practice³.

We all want to reduce neonatal mortality, but the evidence does not show that a national screening programme, never mind sporadic screening in pharmacies, would be effective in reducing deaths from GBS infection.

UK National Screening Committee key findings^2,3

Carriage of GBS changes with time.
- A woman may be carrying GBS when screened at 35–37 weeks, but it may no longer be present at labour.
- Up to 33% of women positive for GBS during their third trimester were GBS negative at term and would be unnecessarily treated with antibiotics in a universal screening programme. In addition, these women may experience unnecessary psychological harm as a result of this false positive diagnosis.
- Up to 12% of women changed from GBS-negative to positive. These women would be inappropriately reassured that they were not carrying GBS and would not receive antibiotics (although see section below concerning the effectiveness of this intervention).
There is no way to predict which babies will be affected by GBS and which will be born without complications.
Treatment for preventing GBS in babies is giving antibiotics to the mother during labour.
- There is serious concern that large numbers (tens of thousands) of women will be offered and take antibiotics when they do not need to. The long-term effects of antibiotics for mother and baby are unknown.
It is not clear whether benefits associated with screening outweigh the harms for the majority of the population.
The proportion of babies affected by GBS in the UK is similar to the level reported in countries that have introduced screening.

National screening problems³
If a national screening programme was introduced, and all 718,126 women pregnant at 37 weeks in the UK each year were tested for GBS colonisation in the third trimester of pregnancy:

Around 150,806 would test positive and be offered antibiotics during labour through a drip.
If they had not received treatment, 333 of these 150,800 women (0.2%) would have had babies that developed GBS, as the test is inaccurate for predicting GBS infection in the baby.
- The remainder (99.8%) would receive unnecessary treatment.
The short or long-term harms to the mother or baby from giving antibiotics to the mother during labour are unknown.
- It is uncertain how many of the 150,800 treated women and babies might be harmed.
It is unknown whether giving antibiotics to women in labour with a positive GBS screening test reduces the number of babies dying from GBS.

And according to NSC most of the deaths and long term problems from GBS are in babies who would not be helped by screening. For example, premature babies are born before screening would take place and are often affected by other conditions which increase the risk of ill health. It is estimated that around 65% of deaths from GBS are found among these babies⁵.

In addition to these clinical considerations, cost of a national screening programme is an important consideration. However, a Health Technology Assessment concluded that it was unlikely to be cost effective⁹.

So, is purchasing a £35 test from a pharmacy the answer? No, because it is no better at identifying women/babies who would benefit from antibiotic treatment. Instead, it just passes the cost of the test onto (possibly frightened) mothers, who may go on to spread this concern to other women in their peer group, thereby potentially increasing the number of inappropriate interventions.

Furthermore, provision of this test in its current format in pharmacy does not meet the Wilson and Jungner criteria — the important features of any screening programme¹⁰.

Problems with treating⁵
Aside from the fact that it is estimated that between 17,000–25,000 women would need to be treated with IAP to prevent one death of a baby from early onset GBS, the following also need to be considered:

Effectiveness — there is limited evidence on the effectiveness of antibiotics in preventing the most severe outcomes of early onset GBS (death and disability).
Antibiotic resistance — this is increasing. Treating large numbers of people to try and reduce the risk of a very rare condition could impact the effectiveness of antibiotics for more common life-threatening conditions.
Allergic reaction – antibiotics can cause allergic reactions in labour and this can be life-threatening.
Long term effects on the newborn — antibiotics used in pregnancy and labour have been linked to increased obesity and asthma and other serious medical conditions.
Limited effectiveness in important groups – antibiotic treatment in labour does not reduce late onset GBS infection, or GBS in premature babies.

Time to think again
In summary, we don’t know if a national screening programme would do more good than harm. On that basis, should pharmacies be offering Strep B home testing kits?

It may be that those offering it think it is a noble enterprise – it’s hyped as saving babies after all. But, given the facts, it is not justified based on the currently available evidence.

The stress and anxiety of worrying pregnant women about it, the potential prescription of and administration of antibiotics of unproven benefit (and possible adverse effects), the risk to the professional reputation of pharmacists of providing a test (which is not recommended by the UK NSC) for the commercial gain of pharmacy contractors even when supplied in all good faith — at worst, it could be seen as taking advantage of frightened women, and what about women who can’t afford it?

Ideally, we need to identify those at most risk of having a baby that develops GBS, not take a one size fits all approach, and perhaps the ongoing trials on a Strep B vaccine could ultimately offer a better alternative.

But, in the meantime, pharmacies need to seriously reconsider this and other ‘screening services’ (such as the PSA test), or continue to fly in the face of current evidence and expert opinion, and get caught up in providing services dictated by tabloid headlines, emotions, and the bottom line instead of evidence. Pharmacy’s continual propensity to supply non-evidence-based products risks seriously damaging the reputation of the profession and giving our detractors further ammunition with which to attack us.

Dr Joseph Bush is a Senior Lecturer in Pharmacy Practice at Aston University*
Ross Ferguson is a clinical author, pharmacy and healthcare writer

*writing in a personal capacity

References

Pharmacy strep B testing: Noble cause, or an own goal for the profession?

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