School "bubbles" aimed at restricting the spread of Covid-19 infections should not be "significantly higher" than 30 pupils, says Derbyshire's public health expert.

Over the past few weeks dozens of schools across the county and city have sent hundreds of students back home, days after returning from summer break, due to a small number of confirmed infections.

In some schools, notably secondaries, leaders have chosen to send entire year groups home due to at times a single case of Covid-19.

Dean Wallace, Derbyshire County Council's public health director, has warned that bubbles which are of an unviable size ought to be reviewed. He agreed that pupils being sent home for two weeks at a time on a regular basis was not sustainable.

He also urged employers not to put staff who must self-isolate, while awaiting a test or after testing positive for Covid, at a disadvantage and losing out financially for doing the right thing.

Mr Wallace told the Local Democracy Reporting Service: "We have had people getting tested just to see if they have it (Covid-19) or not, we have had people getting tested because they think they might have come into contact with someone who might have had it and we have had whole school classes going to get tests because one child might have Covid.

"We need to be prioritising testing for key workers and people who are symptomatic, we need to reign this in.

"There is an issue with some of the size of the bubbles and how they have been interpreted that does need to be worked on.

"A bubble that is significantly higher than say 20 or 30 creates a whole number of repercussions and you have to think that this virus spreads mainly in close distances, so it is very unlikely that one child would have 100 or so close contacts, it is likely to be much smaller than that.

"That refinement needs to happen. That should come as more people get used to it.

"We are walking a fine line in all of this. We need to make sure that the bubbles are appropriate and that risk assessments are robust to determine who needs to self-isolate following a confirmed case. That has to work well and we need to err on the side of caution.

"I think things will improve but the schools can only do so much, they can't control what happens out of the school and what we are seeing is cases found in schools are linked to transmission outside, in the community, and then being brought in. We are not seeing any sustained transmission in school.

"I'm not saying that won't happen at some point in the future but it points to what people are doing outside of the school is the cause, people need to follow the guidance all of the time, such as reducing physical social contact and absolutely never going within two metres of another person outside of your household.

"Treat anybody outside of your household as if they have got Covid-19 and don't go within two metres of them, and if everybody can do that, as difficult as that is, it would get us to a better position in terms of infection rates and spread.

"If everybody outside of the school does the social distancing and the rest of the measures, the risk in the school becomes much less, it would be massively reduced.

"School can be a safe haven and offer some normality and the risk in school needs to be counterbalanced with the risk of long-term mental and physical damage to children.

"A lot of the transmission is coming from younger people meeting outside of school and it spreading back to vulnerable people. This virus will find the vulnerable people, we can't let it run rampant in one age group.

"We have seen the virus moving between households through community interactions, not in specific settings.

"We have to have conversations with our kids about how they act around others and around their grandparents. None of this is easy, but I'd rather have those sorts of conversations now and do that for potentially the next six months than have some serious repercussions affecting parents, grandparents and in-laws that lasts with our kids for their lifetime.

"Everything we do impacts on someone around us and we can't just think of ourselves as an island and doing what we want with our freedoms, this virus will spread and will rip through the population."

Mr Wallace said: "The message to employers is ensure that where staff are being asked to self-isolate that employers continue to make sure those staff don't suffer in terms of their wages and salary while they are waiting (for a test or results) and that staff take on that responsibility to self-isolate until they can get a test and in the absence of a test, self-isolate until that period of 10 days has passed.

"It gets really complex when people on a minimum wage are not able to self-isolate and we need to make sure people are not unfairly punished for doing what's right for their health and the health of the people around them.

"We have seen in Derbyshire that people who have symptoms have not self-isolated and we have seen that having a negative impact in terms of spread happening in various parts of the county

"We are aware that some people have symptoms who have had tests and while waiting for results have carried on as normal and have only decided to self-isolate on confirmation from the test. That's not where we want to be. Assume it is Covid until you find out it is not. If you have symptoms, isolate."