Screening of mothers to protect newborns

A rapid test to determine whether a woman in labour is infected with Group B Strep, which could potentially be harmful to the newborn if left untreated, is being developed at NUIG

When a woman is in labour, the bacteria that live in her birth canal tend not to be uppermost in her mind. But if she carries a type of bacterium called Group B Strep, her baby could pick it up and be at increased risk of conditions like pneumonia, blood infection and meningitis.

"Around 20-40 per cent of women carry the organism naturally, and there's a low but measurable risk of the organism being transmitted to the baby when it is being born," says Prof Terry Smith, director of the National Centre for Biomedical Engineering Science at NUI Galway, who is developing a new, rapid test for Group B Strep in women during labour.

"In Ireland unless there is a specific reason to test for the organism, women aren't tested, whereas in the US they have now recommended screening of all pregnant women in late pregnancy," he explains.

Where the test is offered, the current screening approach means that women who are around 35 to 37 weeks pregnant (the due date is usually set at 40 weeks) have a vaginal swab, which is then cultured to check for the bacterium. Such screening has been associated with a "significant reduction" in Group B Strep-related problems in newborns, according to Prof Smith. But he notes there are some difficulties with screening for the bug in late pregnancy instead of during labour.

"At 35 or 37 weeks a woman might come up negative, but she may be positive when she's going into labour. Or for some reason the test may not pick it up," he says. "You can also get problems if a woman is positive at 35 to 37 weeks and she's given antibiotics at delivery, but it may be that she was negative at delivery after all. So she may have been given antibiotics that she didn't need."

The ideal approach is to screen for Group B Strep when the woman is in labour, but the standard microbiological routine of growing up cultures from the swab takes three to five days to give an answer, which is thankfully far longer than most labours last.

So the NUIG team has come up with a way of quickly screening for signature stretches of DNA in the bacterium. Headed by Prof Smith, Dr Tom Barry of NUIG's department of microbiology and Dr Majella Maher, the researchers have identified a part of the organism's genetic code that uniquely identifies it. They are now working with Beckman Coulter to produce a one-step-device where a swab sample can be put into the machine, and, within around 60 to 90 minutes, there's a yes-or-no answer to the question of whether the bug is present.

A similar device has already been FDA-approved, but they hope theirs will be easier to use in practice, says Smith.

"The big advantages of the labour-ward test are that you are doing the test at the time when the woman is in labour and the time when you need to know whether you need to give antibiotics," says Prof Smith, whose work is funded by Enterprise Ireland.

"So, literally as soon as they come in, women can have the swab taken and the analysis is initiated. Then an hour or so later there's a result, and if necessary they are given an antibiotic at that stage."

The sample is first treated, to smash open any bugs that are present and to release the DNA, then the test looks for any identifying stretches. If they are present, the test multiplies them up, like a molecular photocopier, to millions of copies. Then specific probes can highlight the stretches and alert the reader to their presence.

The instrument can also be used to test for other organisms by looking for their specific genetic signatures, says Smith: "Equally you could have this [device] around the intensive care unit and you could be monitoring for septicaemia bacteria in the blood or MRSA."