Clubs in the English Football League recorded 112 positive tests for coronavirus among staff and players during a week of testing.
A total of 66 EFL clubs underwent mandatory testing for the first time since November, and it has revealed the extent to which Covid is spreading in the game.
League officials and clubs were braced for a high infection rate after more than 50 matches in the EFL have been postponed in recent weeks and a large number of cases reported.
However, the results show that while there are hotspots, with three clubs accounting for 35 cases, many clubs have just one or no positive tests. The remaining six clubs will be tested before their next game.
There has been further disruption ahead of this weekend's FA Cup third round ties, which have seen some clubs forced to field youth teams and Shrewsbury Town's game with Southampton called off after an 'astronomical' outbreak at the League One Club.
The EFL tested 3,507 players and staff at 66 clubs, returning 112 positive cases, an infection rate of 3.2%.
“The current strain has wiped right through our staff,” said Brian Caldwell, Shrewsbury chief executive, who is not revealing the exact number of cases. “The results we got back on Tuesday were quite astronomical, we were all really concerned.'
In the Premier League, clubs are now tested twice a week. Forty players and staff tested positive for Covid in the latest rounds of testing in the top flight this week, double the number of the week before and the highest figure to date.
Some 2,295 people were tested and the infection rate was 1.7%. In addition, four Premier League games have also been postponed due to Covid.
The results come amid growing pressure to suspend football, fuelled by the number of virus outbreaks at clubs and the the actions of high profile players who have ignored Covid restrictions and attended or organised parties during the festive period.
However, the EFL insists a suspension of matches is not on the agenda and the results vindicate their approach.
In a statement, the EFL’s Medical Advisors Dr Richard Higgins and Dr.Subhashis Basu said the infection rate in the clubs reflects the spread of the new variant of Covid nationwide.
'The low reported numbers across the overwhelming majority of clubs means we remain confident that our protocols continue to mitigate against the spread of infection as intended.
“The protocols are allowing us to continue playing fixtures as scheduled but we cannot be complacent, which is why recently enhanced matchday and non-matchday COVID protocols have been issued to underpin the re-introduction of a league-wide testing programme which commences next week.
“Medical advice continues to support that following these protocols is the most successful route to mitigating against the spread of infection.”
Covid protocols in the EFL have not required weekly testing this season. Testing has taken place periodically, but clubs are required to give a test where a player or staff member has symptoms.
The relatively infrequent tests in the EFL have led to concerns that coronavirus may be spreading in clubs unchecked, particularly where people are affected but have no symptoms.
The emergence of mutant Covid, which spreads more quickly, has coincided with an increased number of cases and sharpened those fears.
In response, the league has tightened protocols, with players told they cannot have showers after training unless they live more than an hour away - they must turn up and leave in their kit and access to indoor areas is restricted.
In addition, as revealed by Sportsmail, EFL clubs will begin twice weekly testing for Covid next week.
The tests will use lateral flow devices which are less accurate than the PCR tests in use in the Premier League and used for the mandatory tests undertaken in the EFL this week.
While less accurate, lateral flow tests are cheaper and much quicker to administer. The £5m cost of the tests is being covered by the PFA.
Calls for a suspension of football have been fuelled by controversies surrounding leading players breaking Covid rules.
Tottenham's Sergio Reguilon, Erik Lamela and Giovani Lo Celso partied with West Ham's Manuel Lanzini on Christmas Day, breaking strict Tier 4 rules about gatherings. Spurs have fined their players but allowed them to continue playing.
Crystal Palace captain Luka Milivojevic played after breaking Covid rules at a New Year's Eve party with Fulham's Aleksandar Mitrovic and Benjamin Mendy has not be taken out of Manchester City's squad despite hosting his own New Year gathering.
There has been further controversy in the women's game, where Manchester City's match at West Ham and Arsenal's game against Aston Villa have been postponed. City and Arsenal players tested positive for Covid after travelling to Dubai for a break over Christmas.
Former FA chairman David Bernstein has said he reluctantly supports a shutdown and it has emerged this option was under discussion in government, prior to Boris Johnson's announcement of a nationwide lockdown on Monday.
Fulham midfielder Kevin McDonald, 32, took to social media to claim players are being treated like 'guinea pigs' by allowing games to continue.
On his Instagram story, McDonald fumed: 'How many more outbreaks and training ground closures until football needs to stop!!!!
'Shambolic!! Literally treated like guinea pigs!!!'
Additional testing should help reduce the spread of Covid in the EFL, but it only helps if protocols are rigorously enforced and concerns have been raised that some clubs are still not taking the problem seriously.
Sportsmail has been told of the lengths some clubs have gone to, since the mandatory Covid checks stopped ahead of this EFL campaign, in order to keep the full picture of the virus spread under wraps and allow them to continue playing games.
One club in League One is understood to have pressed ahead with a game — putting their opponents at risk — despite knowing a number of their players and staff were affected. Tests soon after revealed an outbreak at the club, which led to the postponement of a number of their subsequent matches.
On Thursday, Gordon Taylor, chief executive of the Professional Footballers' Association, warned players to stop hugging during goal celebrations and after matches and to observe social distancing on the pitch, in an attempt to slow the rapid spread of coronavirus in clubs.
Taylor's intervention came after intense celebrations at high profile games, including a huge group hug among Manchester City 's players after they knocked rivals Manchester United out of the Carabao Cup in Wednesday's semi-final at Old Trafford.
But similar scenes are witnessed at almost every game throughout each tier of the league, including in clubs where coronavirus has spread.