Visitors are in no danger
By Matthew Rollosson
Tacoma-Pierce County Health Dept.
Tacoma-Pierce County Health Department continues to support a tuberculosis investigation among staff at Point Defiance Zoo & Aquarium after some staff members who work with and around elephants tested positive for latent tuberculosis infection last month. No one has tested positive for active TB.Tuberculosis is very difficult to catch, and it’s safe for you to visit the zoo.
What you should know about TB
Part of our role in managing every case of active pulmonary tuberculosis is finding other people who might have been infected by the person with TB. This is called a contact investigation. State law requires us to do it.
Tuberculosis can affect any part of the body. It most often affects the lungs. People with active TB in the lungs are infectious; they can transmit the bacteria that causes TB to other people. Like measles, TB is transmitted by tiny respiratory droplets that can remain suspended in the air for hours. But unlike measles, it is not easy to get and transmission requires prolonged close contact with someone who has active TB.
A contact investigation begins with the people who have spent the most time with a person with active TB. These are usually people who live in the same household as the case. Contact investigation is one of the ways we determine how infectious a person with active TB is. If the people who live in the same house test negative, that tells us the person with TB is not highly infectious, so we don’t have to look far for other people who might have been infected. If the household contacts are infected, then we start looking at other people who have spent time with the case; family members who live outside the household, coworkers, classmates, or other social contacts.
Most people who are exposed to the bacteria that causes tuberculosis do not become infected. I’ve been exposed many times over the 27 years I’ve been a nurse and my TB skin test has always been negative. Most people who are infected do not develop the disease. Infection without TB disease is called latent tuberculosis infection (LTBI). People with LTBI are not sick and cannot transmit the bacteria to others. About 10% of healthy people with LTBI will develop TB disease at some point in their lives. TB is highly treatable with antibiotics. People with LTBI can take medication to reduce their risk of developing TB disease.
Less exposure, lower risk
Because tuberculosis can be transmitted between people and elephants, zoos test both elephants and the people who work in close, prolonged contact with them every year. This year, several people who work with and around the elephants at Point Defiance Zoo & Aquarium had positive tests for latent TB infection. All of them previously had negative screening tests and all of them have since had chest X-rays to rule out active tuberculosis disease. They have latent TB, are not sick, and cannot infect anyone else. We are waiting for test results to determine if Hanako and Suki, the elephants at Point Defiance Zoo, are infected.
As we would with any other contact investigation, we are now looking for other people who might be infected. That means people who spent less time in the elephant barn than the people who have had positive tests so far. So far, the people who have tested positive for latent TB are those who have had close, prolonged contact with the elephants or spent a significant amount of time in the elephant barn They are the people we consider at highest risk. Now, out of an abundance of caution, we are testing people who have spent significantly less time in the elephant barn and have much lower risk.
We don’t expect to find anyone with active tuberculosis, but we haven’t ruled it out. We usually don’t see this many people infected among household contacts. When we do, it’s someone who has advanced disease and is very sick.
The screening tests can take weeks to develop after exposure, so people who test negative now will need to be retested in eight weeks.
In the meantime, continue to enjoy visiting Point Defiance Zoo & Aquarium. There is no risk to the public. State and local health officials have inspected the zoo’s elephant exhibit and determined it is safe for visitors.
Learn more about tuberculosis at www.tpchd.org/tb.