So far one person who attended the mass anti-racism demonstration in Amsterdam on June 1 has been identified as having coronavirus, according to local health board figures.

However, officials say, the patient did not have symptoms at the time of the demonstration and it is unclear, as yet, where and when he became infected.

Although the maximum incubation period of two weeks is now over, this does not mean other people who were had the demo did not have the virus, the health board said.

And experts have told broadcaster NOS that the next time a large group of people get together at close quarters it could be a different story.

Experts

‘The more people who gather closely together, the greater the chance that one of them has the virus,’ Erasmus virologist Marion Koopmans said.

‘We know that the chance of infection is smaller outside than indoors, but it not zero,’ Utrecht teaching hospital epidemiologist Patricia Bruijning told the broadcaster. ‘We were lucky. But if you repeat this experiment a number of times, it will go wrong once. I really would avoid large events.’

Waste water

Meanwhile tests on waste water in Amsterdam on June 10 have shown a sharp rise in the presence of coronavirus particles. In the week prior to June 10, scientists found four particles per millilitre, but a week later that had risen to 40.

This does not mean there has been a major rise in infections in the capital, because the quantity depends on how seriously people have been affected and at what stage the illness is, spokesman Gertjan Medema told the website.

There has also been an increase in coronavirus particles in Amersfoort, but a drop in Utrecht and The Hague, Medema said.

Spike

In Dordrecht, however, a local spike last week has now been put down to faulty lab equipment.

Fifteen people who were told they had tested positive for coronavirus have now been send a second letter revising the findings.

Doctors had sounded the alarm after there was a rise in positive tests in the city following the introduction of mass testing on June 1.