In just a few weeks, five people have been treated for severe pneumonia following close contact with birds, reports news agency TT.
The five cases are spread out over different locations in the Gothenburg area and South Älvsborg. It's believed that people have probably become infected when cleaning a bird table or in other ways of close contact with birds.
"It is usually not more than a dozen cases in the entire country for a whole year. So five cases within a few weeks is much more than it should be," says Leif Dotevall, assistant medical officer in Västra Götaland.
"We do not know what it is, but it is probably that more birds right now carry the infection than usual," he says to TT.
He calls for extra caution, no matter how harmless the little birds that visit bird tables may seem to be.
"There is a well known route of infection from inhaling dust from dried bird feces, both from wild birds or from domesticated birds," he says.
"One sweeps or brushes and it brings up dust. It is absolutely wrong. One should clean with soapy water, and if, for example, one removes a bird's nest, then you should wear a mask. And wash hands thoroughly afterwards."