In 2020-2021, a total of 52 cases were recorded of human ornithosis (parrot fever), which is caused by the zoonotic bacterium Chlamydia psittaci. The bacterium may be transmitted to humans through direct contact to birds or through inhalation of dust or vapourised infected material from feathers, faeces or secretions. Human disease cases are notifiable to the Danish Patient Safety Authority (DPSA) and to the Department of Infectious Disease Epidemiology and Prevention, Statens Serum Institut (SSI). Veterinary ornithosis is notifiable if C. psittaci is suspected in a flock of birds. C. psittaci is found in faeces and in secretions from the nostrils and beaks of birds; it tolerates drying out and can remain infectious for a prolonged period of time.
Human diagnostics and clinical presentation
In the 2020-2021 period, a total of 49 persons were notified as having become infected in Denmark and two persons were notified as having become infected abroad. For one person, the country of infection was unknown. Among the notified cases, 39 were men and 13 women. The median age was 61 years (range 29-85 years). No patients died within 30 days after being diagnosed with ornithosis in the period.
More data are available in Danish at ssi.dk/data, select “Ornitosis” under “Individuelle anmeldelser” (Danish for “individual notifications”).
Analyses for the 52 patients were conducted at all Danish departments of clinical microbiology, and the patients’ residences were scattered across all Danish areas, but with more cases being observed among men living in West and South Zealand (9), on the island of Funen (8) and in South Jutland (6), Figure 1.
Figure 1 presents the distribution by sex and area of human, clinically notified ornithosis cases and Danish residence shares in the 2020-2021 period. As appears, a predominance of men with private bird flocks was observed.
Sources of infection in human cases, 2020-2021
In 2020-2021, a total of 25 clinically notified persons were registered as having become infected in connection with private flocks of birds, including pigeons, chickens, geese or small pet birds. An additional seven cases were notified as possibly having become infected through other contact with birds, including wild birds. For the remaining cases (n = 20), the mode of infection was unknown or not stated, even though two persons may have become infected occupationally.
Infection tracing for human and veterinary cases
The SSI and the University of Copenhagen jointly carries responsibility for the Danish veterinary preparedness service (Danish Veterinary Consortium, DK-VET), and samples from birds suspected of carrying the disease are submitted to the SSI for analysis.
The SSI has analysed 190 veterinary samples for C. psittaci DNA in 2020 and 937 samples in 2021, Table 1. These samples were primarily submitted for infection tracing in connection with notified human cases and suspicion of outbreaks. A limited number of cases (4) concerned bird exports.
In the summer of 2021, a human case of infection was caused by purchasing pet birds, which triggered comprehensive nationwide tracing efforts. The investigation conducted has been described in the article “Ornithosis outbreak in pet birds in 2021” in the Danish Veterinary Journal (Dansk Veterinærtidsskrift). Just in this outbreak, a total of 760 samples from various species of bird and from different bird flocks were submitted for diagnosis at the SSI. A total of 81 samples tested positive to C. psittaci, corresponding to 10.7% of the samples tested. In addition to the index person, no further human infection was detected or notified in relation to the outbreak.
Prevention in animals and humans
In humans, ornithosis is prevented by wearing gloves and a respiratory mask during contact with sick birds, and by frequently cleaning and disinfecting the floor of the cages. Read more about the prevention of ornithosis in humans here.
On suspicion of ornithosis in a flock of domestic birds, the veterinarian contacts the veterinary preparedness service which forms part of the Danish Veterinary and Food Administration (DVFA), whereafter the bird flock is placed under public monitoring. Similarly, if transmission to a person is confirmed, the DVFA will also suspect ornithosis in the flock of birds concerned.
This annual report is also described in EPI-NEWS no. 20b/22.