By: Heather Williams

Investigations are still underway in the Orange County area Legionnaires’ disease outbreak continues to puzzle investigators.   The case count has risen to 15, leaving 2 dead.  Of the 15 who were infected, 11 had visited Disneyland between late August and October.  The investigation lead Orange County health officials to cooling towers at the Disneyland park.  Two towers were shut down due to elevated levels of the bacteria Legionella.  No further cases have been reported since the cooling towers were closed.  With the two Legionnaires’ deaths occurring with individuals who had not visited the park, investigators continue to look for answers.

Healthcare providers are looking for answers as well.  How is Legionnaires’ disease diagnosed?  First, the symptoms must be identified.  Then specialized tests are ordered to detect the presence of the bacteria.  Once results have been obtained, an informed diagnosis can be presented, allowing more specific treatment options for the patient.

What is Legionnaires’ Disease

Legionnaires’ disease is the common name for legionellosis or infection with the bacteria Legionnella pneumophila, found in water systems.  It is estimated that 10,000 to 18,000 people in the United States are infected with the Legionella bacterium each year.

Often, Legionnaires’ disease goes undiagnosed due to the similarity to symptoms of pneumonia and the most susceptible population being also more susceptible to pneumonia.  Many times a patient presenting symptoms such as a cough that can be either dry or productive (with or without bloody sputum), headache, high fever accompanied by chills, weakness or fatigue, muscle aches, chest pain, shortness of breath, lethargy, and/or mental changes such as confusion are treated for pneumonia and the additional symptoms.  For Legionnaires’, symptoms often include watery diarrhea, abdominal pain, nausea or even changes in heart rate or a lower blood pressure.  Unless the physician expects Legionnaires’ disease as a diagnosis, the very specific tests to determine if the person in fact has been infected with the legionella bacteria if often not performed.  Many times the person can recover without the specific treatment for Legionnaires’ disease, however the outcome and speed of recovery will be much better if appropriate treatment is given to fight the bacteria.

Who Should be Tested for Legionnaires’ Disease?

A patient presenting symptoms of both pneumonia and gastrointestinal issues such as diarrhea and/or nausea, should be tested for legionella; particularly if the patient also has mental changes such as confusion.

The Center for Disease Control and Prevention (CDC) recommends testing the patient for Legionnaires’ disease if the patient is in Intensive Care and has severe pneumonia or has pneumonia and a weakened immune system.  The patient should be tested for Legionnaires’ disease if they have been treated with antibiotics, but symptoms have not resolved.  If the patient has travelled away from home within the past two weeks and then became ill they may have came in contact with Legionella pneumophila and should be tested for Legionnaires’.  Additionally, if the patient may have acquired pneumonia in a nursing home or hospital, they should be tested for Legionnaires’.  Of course, if the patient has pneumonia during a legionellosis outbreak, they should be tested for Legionnaires’ disease.

Tests for Legionnaires’ Disease

Health care providers have four common ways of detecting the Legionnella bacterium to diagnose legionellosis or Legionnaires’ disease.  These include antigen testing, culture, antibody testing, and genetic testing.  A urine or respiratory sample is required to complete these tests.  The CDC suggests antigen and culture testing to diagnose Legionnaires’ disease.  Additional testes such as sputum culture, gram staining, complete blood count, and chemistry panels may also be ordered to help give a bigger picture of the patients’ overall health and any other ailment the body may be fighting.  An additional blood sample may be required for these tests.

Antigen Testing

Antigen testing is often performed as an initial test if Legionnaires’ is suspected and provides a rapid result.  This testing is specific to Legionella pneumophila and detects one of the bacterium’s proteins.  This can be found in the urine and sometimes other bodily fluids, but urine is the most common sample used.  A negative test result does not necessarily rule out the infection, as it only detects the serogroup 1 of Legionella pneumophila, though most cases of Legionnaires’ disease in the United States are a result of this specific bacteria.  This is a quick method to get a yes or no answer.  The “yes” allows the health care provider to look into specific treatment right away.  The “no” just means that the physician will continue the diagnostic process, which will likely include a bacterial culture regardless of the positive or negative outcome of the test.

Bacterial Culture

To confirm the presence of Legionella bacteria and diagnose Legionnaires’ disease, a bacterial culture is often performed on sputum.  Sputum is a medical term for what someone coughs up as a result of respiratory illness.  The laboratory uses a special nutrient media that encourages the growth of Legionella and discourages the growth of other bacteria.  For this reason, it is considered the “gold standard” and a confirmation tool to diagnose the infection.  This test takes a little bit of time, though a positive culture may grow between 48 and 72 hours.  Negative cultures are held for seven days before a final result is reported to be sure no growth occurs.

Antibody Testing

Antibody testing using Direct fluorescent antibody (DFA) staining for Legionella species is another diagnostic tool a physician may use to diagnose Legionnaires’ disease.  This is a rapid test that uses a specialized stain that attaches to antibodies specific to Legionella bacteria.  This test can provide results in as little as 2 to 4 hours.  This test is not often performed because it is not as sensitive as other methods and requires a very large sample to perform.

 Genetic Testing

While not widely used, genetic testing can be performed on respiratory samples to detect the presence of Legionella species.  This type of testing uses polymerase chain reaction (PCR) to detect genes found only in Legionella bacteria.  This specialized test can detect many species of Legionella at the same time.  At this time, many diagnostic laboratories do not perform PCR and those that do have particular bacteria that they are looking for.  This is a costly diagnostic test to maintain, so many labs refer samples to local health departments or state labs if necessary.