Legionnaires disease is a respiratory condition caused by Legionella pneumophila. It is best diagnosed by organism culture; however, the organism is difficult to grow.
Detection of L. pneumophila in respiratory specimens by means of direct fluorescent antibody (DFA) technique is useful for rapid diagnosis but lacks sensitivity when only small numbers of organisms are available. Serologic tests should be used only if specimens for culture are not available or if culture and DFA produce negative results.
Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions. Label the specimen with the patient’s name, date, and tests ordered and place in a biohazard bag for transport to the laboratory.
Follow-up testing is usually requested 3–6 weeks after initial symptom appearance.
Alert the patient that a urine specimen may be required if antigen testing is indicated.
A dramatic rise of titer levels to more than 1:128 in the interval between acute- and convalescent-phase specimens occurs with recent infections.
Serologic tests, to be useful, must be performed on an acute (within 1 week of onset) and convalescent (3–6 weeks later) specimen.
Serologic testing is valuable because it provides a confirmatory diagnosis of L. pneumophila infection when other tests have failed. IFA is the serologic test of choice because it can detect all classes of antibodies.
Demonstration of L. pneumophila antigen in urine by ELISA is indicative of infection.
Pretest Patient Care
Assess clinical history and knowledge about the test. Explain purpose and procedure of blood test.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing, as negative results do not rule out L. pneumophila.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.