Soft drinks shouldn’t be ‘tested’ with lateral flow tests and asymptomatic transmission is not ‘quackery’

A post on Facebook shared over 1,000 times makes a number of false claims about testing for Covid-19 and transmission from people who don’t have symptoms. It also includes an image of seemingly positive lateral flow test results achieved using cola and orange juice.

Substances like cola and orange juice will break lateral flow tests

The Facebook post includes an image of two positive lateral flow tests: one which the post indicates has been tested using cola, and the other with orange juice. It is not clear exactly what the post is trying to suggest by including this image, but it implies that this is evidence that lateral flow tests are somehow flawed or untrustworthy. 

We have written many times before about the fact that using substances such as fruit, soft drinks, diluted cordial, ketchup and even tap water can produce a positive result on lateral flow tests. This doesn’t mean that the tests are inaccurate or can’t detect SARS-CoV-2, but that these substances have broken the tests and produced a meaningless result. 

Dr Alexander Edwards, associate professor in Biomedical Technology at the University of Reading, previously told Full Fact: “If you completely ignore the manufacturer’s instructions or in fact use the test for something completely different, then you shouldn’t really be surprised if you get a silly result.”

It’s not correct that “asymptomatic transmission is quackery”

The Facebook post falsely claims that “asymptomatic transmission is quackery”. As we have written before, the role of asymptomatic transmission of Covid-19 was uncertain earlier in the pandemic, and initially suspected by some to be small. 

However, its role in the spread of Covid-19 has become clearer. For example, the World Health Organisation now says “Whether or not they have symptoms, infected people can be contagious and the virus can spread from them to other people”. 

A study published in Nature in June 2020, which studied the town of Vò, Italy, for example, showed that around 40% of positive cases were in people who were asymptomatic, and that these asymptomatic people had a similar viral load (concentration of virus) as symptomatic people. Other meta analysis studies (which analyse the results of several studies together) have shown asymptomatic infections make up between 17% and 20% of cases. However, there were large ranges within the studies. 

And studies have shown that while people who are asymptomatic may transmit Covid-19 less frequently than their symptomatic counterparts, they do appear able to spread Covid-19. Exactly how much asymptomatic transmission contributes to overall transmission is difficult to pinpoint, as this depends on the activities an asymptomatic person undertakes, their environment, whether individuals truly show no symptoms or are presymptomatic, and other factors such as vaccination and which variant of Covid-19 they are infected with.

It’s not necessarily the case that “more testing equals more cases which equals more restrictions”

While it’s not completely clear what the Facebook post means here, it’s certainly the case that testing allows more accurate counting of cases, which in turn allows health authorities to try and limit the spread of the disease, but it doesn’t impact how many cases actually exist in the population. 

In addition, as we have written about before, the number of positive cases isn’t the only measure used to understand the spread of the virus. Experts have previously told Full Fact that other factors, such as test positivity (the proportion of tests that are positive), changes in testing volumes and other measures are also considered.