A paper in Epidemiology and Infection (Belchior et al 2011) describes an outbreak of psittacosis (Chlamydophila psittaci infection) in people who attended a bird fair in western France in 2008.

The investigation started off with the identification of the bird-associated disease in three people at a local hospital. All three were hospitalized with respiratory disease, and all had attended the bird fair.

  • A critical step in diagnosis of psittacosis and recognition of outbreaks is knowing about bird contact. If bird contact isn’t questioned, psittacosis is unlikely to be considered. Too often, physicians don’t inquire about animal contact, which limits their ability to detect zoonotic diseases. In this case, a survey on psittacosis was underway, which may have helped.

This finding led to an investigation of the fair to determine what happened and make sure there were no other unidentified cases.

The fair lasted one day, and had 83 exhibitors, 1500 birds and around 600 visitors. The investigators ultimately identified two confirmed cases of psittacosis in people who attended the fair, along with two probable and 44 possible cases. (Possible cases were people who developed respiratory disease and were exposed at the event, but did not necessarily have any diagnostic testing done to confirm the cause).

The reported disease characteristics were pretty typical:

  • Fever in 96%
  • Pneumonia and cough in 63%
  • 98% visited a doctor
  • 23% were hospitalized
  • No one died (psittacosis can be fatal, but is quite treatable if identified in a reasonable time)

Thirty-eight percent (38%) of exhibitors and organizers got sick. That’s a very high attack rate for people casually interacting with a group of (presumably) healthy birds. Poor ventilation may have played a role. The fair was held inside, windows were closed and there was no mechanical ventilation. This might have helped the bacterium build up in the air in the building and result in wider, heavier exposure.

The source of infection wasn’t determined. They were only able to obtain samples from birds from six of the 83 exhibitors, and all 64 tested birds were negative. Chlamydophila psittaci can be shed by healthy birds, and identification of the source isn’t always easy.

It’s not guaranteed that everyone who got sick after the fair had psittacosis. You can’t rule out the possibility that there were only a couple people with psittacosis and a large number with the flu or another disease, but the incidence of disease, type of disease and timing of disease are all quite suggestive.

How do we prevent outbreaks like this in the future? It’s tough to prevent them completely, because you can’t tell that a bird is shedding the bug just by looking at it, and testing every bird before a show is  impractical. Risks can probably be reduced by ensuring proper ventilation, limiting crowding of areas, limiting unnecessary direct contact between birds and people, and improving general hygiene practices.

Thanks to Dr. Doug Powell of BarfBlog for sending the article.

More information about psittacosis is available in our archives.