Coronavirus infections are mainly taking place at home, with outside sources including visiting friends and relatives, work places, schools or childcare facilities.
Of all the people who were tested positive this week, half did not know at all where they could have become infected while the other half had some idea, Nu.nl reports quoting figures from health institute RIVM.
In the week prior to October 13, when bars and restaurants had to close their doors, only 16% thought they knew where they had been infected. That was mainly due to limited testing and tracing at the time.
The RIVM does not distinguish between the type of work places, which, despite calls by the government to work from home, may include offices.
Ruling out bars and restaurants is also putting schools and childcare facilities in the spotlight, with 10.3% of people naming these as the more likely source of infection.
RIVM figures show that the infection rate among secondary school pupils over the last week is higher than that among primary school children.
Children aged between five and nine only made up 1.7% of all registered infections. This went up to 7.8% for children between 10 and 14, while the 10.8% of infections were among teens between 15 and 19.