Starting Friday, Blood Bank Sanquin will test all the blood donations for West Nile virus in 9 provinces, following the latest, fourth, death of a person who received West Nile-infected blood from a Sanquin donor.

Ten people were recently tested positive in the Netherlands, with the total number of infections jumping to 28. Sanquin classifies Overijssel, Utrecht, Gelderland, Noord-Holland, Noord-Brabant, and Zuid-Holland as West Nile risk areas, as all of the infected people were from those provinces. No infections have been reported in Groningen, Friesland, and Drenthe. The three provinces will still be screened.

The donor was infected by a mosquito. West Nile virus originates in birds but is passed to humans by the mosquitos. People can develop flu-like symptoms. However, according to the RIVM, most people notice almost no symptoms. Nevertheless, encephalitis, meningitis, or a polio-like disease can appear in most severe cases.

It is unclear if the person that died was killed by the virus or if they already had existing health complications. Following the deadly transfusion, the donation unit was shut down, so no one else reportedly received the infected blood.