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Revealed: The ‘design flaw’ that leaves coronavirus test swabs too long to fit inside sample vials

Many of the DIY testing kits that are being sent out to households around the country have swab sticks that are too long for the sample bottle they go inside.

The issue may explain why the volunteers at testing centres have reported that many samples are being returned without “the lids screwed on properly”, contributing to delays in patients receiving results and reducing the number of tests processed each day.

The problem is reminiscent of British railway issues such as “leaves on the line” and trains being delayed after encountering the “wrong type of snow”.

The Government is sending tens of thousands of DIY coronavirus test kits to households across the country in a bid to better understand the spread of the disease.

It was eager to get the tests sent out because the moment they are in the post they count towards the Government’s 100,000-a-day test target – something that has been hit on just nine of the 21 days since it came into force on April 30.

But the sticks end up being too long for many of the sample bottles they are supplied with, making it very difficult to close the lid properly and therefore risking cross-contamination.

“It was a huge challenge to then get the lid of the tube on. It took me about five minutes”, said Catherine, 55, who is taking part in the Office for National Statistics Infection Survey.

Her son Tom added: “I had to use all of my strength to shut the cap. It seems like a design flaw.”

The swab sticks are designed with a weak point in the middle which should allow them to be broken in half after use, with the end containing the cotton wool sample supposed to then fit neatly into the bottle.

But it appears that some swab sticks have the break point at the wrong spot along their length, meaning that the sample end must be forced into the bottle or the lid left partially open.

“There seemed to be a single spot where the swab stick broke, and it snapped very easily,” said Catherine. “It took me about five minutes and some considerable force to push the cap in place. Once I had, there was an obvious bend in the swab stick inside the tube.”

Tom, 22, added: “When you break it the swab ends up about two or three millimeters too long to fit easily back in the tube. 

“So I really wasn’t surprised to hear radio reports yesterday that labs are being sent back tests without the cap on.

“If my Grandma got sent one of these tests, I’m really not sure how she’d be able to close the lid properly.”

Prof  Alan McNally, infectious disease lead at the Milton Keynes Lighthouse Lab for Covid-19, said on Wednesday that while the vast majority of samples are processed quickly, “hiccups” were delaying a substantial minority. 

“One of the things that really hold us up is when people haven’t applied the barcodes properly to the sample tubes,” he told BBC Radio Four. “We also get samples where the lid hasn’t been screwed on properly. 

“This means the sample leaks out and we have to try to recover it so we can test it. There will be occasions where it takes longer to test, and usually it’s because of small hiccups like that.”

Nicola Stonehouse, professor in molecular virology at the University of Leeds, added that a lack of a standardised testing kit also contributes to delays – and likely explains why issues around swab tests lengths are not universal, with some users reporting no problems. 

“There’s a lot of variety in the sample tubes that are coming in,” she told the Telegraph. “This means that more human intervention is required to process them, slowing things down. 

“A couple of weeks ago about 20 to 30 per cent of tests arriving at labs needed some form of human intervention – be it because a barcode was incorrectly applied, the lid had come off or the PCR test needed adjusting to fit the size of the test tube.”

“Things are improving, we’re getting more standardisation, but teething issues are expected when you’re building a system from scratch,” Prof Stonehouse added. “If we’d started this process earlier, most of these issues would already have been ironed out – we’re playing catch up.”

This sentiment was shared by Adrian Walker, a lead biomedical engineer at Mologic, which has been manufacturing diagnostics tests for Covid-19 since April.

He told the Telegraph that there was likely to be large variation between the swabs produced by different manufacturers as organisations decided their own approach based on resources available. 

“In my mind – and I’ve been doing this for 40 odd years – different manufacturers do things in different ways and that is why there might be problems with some tests but not others.”

He added that due to heightened demand, some companies were using standard designs for the swabs which can result in issues further down the line. 

“The break point can be specified depending on the size of the tube – or there can be a standard break point which tends to be in the middle of the swab shaft. If the break point is too high – sometimes that happens when using a standard break point measurement. 

“Some of these tests have probably been made in a hurry –  so in some cases standard swab measurements would have been used as they would have been readily available for manufacturers,” Mr Walker said. 

The tubes provided are thought to be supplied by a separate manufacturer. 

A Department of Health and Social Care spokesman said: “More than 2 million people have now been tested in the UK and the vast majority report no issues with the testing process.”

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