Psittacosis closure at Atlanta zoo

Zoo Atlanta has closed its parakeet exhibit after one of the birds died of Chlamydophila psittaci infection. The concern is that this bacterium can cause infection in people (sometimes called parrot fever). Infection of humans is uncommon and usually just causes flu-like disease, but it can be very serious, especially if not diagnosed properly in a timely manner.

The zoo is going to test the flock and decontaminate the facility. The question is, "what will happen if other birds are positive?" Actually, the question probably should be "what will happen when other birds are identified as being positive?"

Chlamydophila psittaci gets the "psittaci" component of its name because it is commonly found in psittacine birds (e.g. parrots, parakeets and other related birds). The dead bird got the bacterium from somewhere, and living communally with other psittacines means that the odds are very good that multiple birds are now carrying it, since birds can carry this bacterium without any signs of disease. Varying carriage rates in psittacines have been reported in different studies, but in some groups (e.g. breeding colonies) rates can be very high.

Concern about the aviary is reasonable, since this bacterium can be spread through the air, mainly through inhalation of contaminated material that's been aerosolized (e.g. dried feces that end up in dust in the air). If there's no direct contact with birds, through, the risk to the public is probably very low. Some management practices can be used to reduce the risk of aerosolization of the bacterium and reduce the risk of exposure of the public. These could include using cage litter that isn't dusty, regular and thorough cleaning of the area and cleaning in a manner that reduces the risk of aerosolizing the bacterium (e.g. wetting things down before cleaning, not using a vacuum unless it has a HEPA filter).

So, what about testing? One of my standard lines is "never do a diagnostic test without a plan to use the results." Hopefully, the zoo has thought about what they'll do with positive results, since it's likely they'll have many.

Testing is a somewhat controversial area. It's been recommended that birds in areas where they will be exposed to a lot of people be tested. That could apply here, depending on how the birds are managed. One issue with testing is it's far from 100% accurate, so it's only one part of the control program and testing limitations need to be understood. Testing makes the most sense in a population of birds that is closed, meaning there are no new birds coming in. That way, a couple of rounds of negative tests can give you pretty good assurance that the group is negative. Positive birds can be quarantined and treated to try to eliminate the bacterium. If most of the group is positive, it makes it pretty difficult to eliminate. A single round of testing or testing and then bringing in new birds doesn't help too much.

Overall, the risk is greatest for zoo personnel who work with the birds and their environment. Good infection control protocols should already have been in place to reduce the risk of disease transmission, but presumably those are being revisited. It's often a controversial subject since use of barriers such as eye protection and an N95 mask are often recommended when cleaning cages, but this is rarely done and there's (reasonable) reluctance to do so because of the rarity of disease, the commonness of the procedures and the fact that people have been doing this for years without these extra precautions. It's a tough area to address and it requires careful consideration of the costs and benefits. Other important points for psittacosis control include avoiding bringing in new birds, avoiding mixing of different groups of birds, checking new birds for signs consistent with C. psittaci infection before bringing them to the facility, quarantining new arrivals and educating people who work with the birds.

One key factor, regardless of what's done, is that people who work with psittacines need to know that they are at increased risk of psittacosis. Their physicians also need to know that they work with psittacines (and that psittacosis is a potential concern). In this situation, people who have worked with the affected bird (and any other bird that might be a carrier) should know to see a doctor if they develop respiratory or flu-like illness.

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