The number of people in hospital with coronavirus has fallen to its lowest level in more than 18 months, latest government figures show.

On Tuesday the public health agency RIVM’s dashboard recorded 349 patients who had tested positive for the virus, the first time since September 2020 that the figure has been below 350. They included 19 patients in intensive care.

However, medical experts have voiced concern that the low level of testing and monitoring is compromising efforts to keep the virus under control.

Virologists Marion Koopmans and Menno de Jong, both members of the now disbanded Outbreak Management Team, have called for sample testing to be carried out to get a better picture of the level of infection.

‘It’s important the surveillance gets under way,’ Koopmans told NOS, while De Jong warned that scientists have a ‘very limited view’ of the spread of infection.

De Jong said random sampling was a quick and easy way to improve the level of information. ‘Park a bus, test a group of people and see how many are infected and what variants are circulating,’ he said.

Since March coronavirus testing has been restricted to people at high risk, such as those over 70, healthcare workers and people with compromised immune systems, as well as those who need proof of recovery in order to travel.

Around 2,000 people a day are currently taking a test at a local health service (GGD) centre, half of whom are found to have the virus. The number of positive tests has dropped by 50% since the start of May and the RIVM’s latest calculation of the R number, which measures the rate at which the virus is transmitted from person to person, is 0.89.

Sewage samples show the number of virus particles per 100,000 people has fluctuated between 250 and 400 during May, 90% lower than in March but higher than a year ago. Hospital cases a year ago were four times higher and there were 25 times as many patients in intensive care with the more severe Delta variant.