European countries report unusual rise in psittacosis infections

filling feeder

Zbynek Pospisil/iStock

Five European countries have reported an unexpected rise in infections involving psittacosis, a respiratory disease from a bacteria known to affect birds, which began in late 2023 and has led to the deaths of five people.

In an outbreak notice today, the World Health Organization (WHO) detailed recent reports from Austria, Denmark, Germany, Sweden, and the Netherlands. In most instances, people had contact with wild or domestic birds.

Affected countries are investigating exposures and case clusters. Only one of the countries—Sweden—had a change in diagnostic testing procedures, a factor that might explain an increase in reported cases.

Psittacosis is caused by Chlamydophila psittaci bacteria, which is known to affect birds. Transmission to humans typically occurs through inhaled particles from respiratory secretions, dried feces, or feather dust. Infections are often mild, but patients can develop a sometimes-fatal pneumonia. The disease is treatable with prompt, appropriate antibiotics.

Many patients were exposed to birds

Austria reported 14 cases from five of its nine states in 2023 and has already reported four cases in 2024. Over the previous 8 years, the country averaged about two cases a year.

None of Austria's patients had traveled abroad or reported contacts with wild birds, the WHO said.

Denmark reported a sharp increase in cases in late 2023 through mid-January. Of 23 cases, 4 were fatal. Seventeen people were hospitalized, including 15 who were diagnosed as having pneumonia. For comparison, the country typically reports 15 to 30 cases each year.

The Danish patients are from three regions: North Denmark, Zealand, and Capital. Investigations found that one patient had domestic birds that tested positive for C psittaci, and 12 had contact with wild birds, mainly via bird feeders.

For comparison, the country typically reports 15 to 30 cases each year, the WHO said. Though most cases are linked to wild birds, several cases each year have no known exposure link, hinting at potential environmental exposure. Plans are under way to assess C psittaci prevalence in Denmark's wild bird populations.

Meanwhile, Germany reported a spurt of five cases in December that brought its 2023 total to 14. So far this year, officials have reported five more cases, some of them clustered around the city of Hanover.

Nearly all Germany's patients had pneumonia, including 16 who were hospitalized. None of the patients had information on exposure to wild birds, but five had been exposed to domestic birds such as parrots, chickens, or breeding pigeons.

Similarly, the Netherlands has reported increased cases since late December, with 21 cases reported so far—twice as many as the number reported in recent years. Infections were reported across the country. All patients were hospitalized, and one died. Thirteen patients had contact with droppings from wild or domestic birds.

Swedish cases on the rise since 2017

Elsewhere, Sweden reported 26 cases from November through December, double what the country typically saw over the same period over the previous 5 years. Cases were spread across 8 of the country's 21 regions, mainly in the southern third of Sweden.

Investigations found that patients often had contact with droppings from small birds, mainly via feeders, though a few may have contracted bacteria from domestic birds such as hens or cockatoos. Unlike the other countries, officials said increasing use of reverse transcription-polymerase chain reaction (RT-PCR) panels for screening may have increased detection. The WHO said Sweden's cases have been trending upward since 2017.

Probes will sort out what's driving rises

The WHO said the increase across all the countries requires more investigation to determine if it reflects a true rise in cases or if the spikes in cases are due to better surveillance and testing.

"While birds that carry this disease could be crossing international borders, there is currently no indication of this disease being spread by humans nationally or internationally," the WHO said.

There is currently no indication of this disease being spread by humans nationally or internationally.

The group added that national surveillance systems are closely monitoring the situation and that lab sampling of wild birds is under way to better gauge the prevalence of C psittaci in wild birds. So far, the human health risk is low, the WHO said.

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