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SPECIAL ARTICLES: Review of Literature: General Infectious Diseases

LEGIONNAIRES DISEASE: A GUIDE TO DIAGNOSIS AND THERAPY

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Infectious Diseases in Clinical Practice: March-April 2002 - Volume 11 - Issue 3 - p 166-167
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LEGIONNAIRES DISEASE: A GUIDE TO DIAGNOSIS AND THERAPY

[Roig J et al. J Resp Dis 2002;23:229]:

The authors review Legionnaires’ disease and the following summarizes their observations with emphasis on the issues that are most clinically important and controversial:

  • Epidemiology: The natural habitat is water including rivers and lakes, although L. longbeachae has been found in soil. Cooling towers have overemphasized as the source of infection and air conditioners have not been definitively implicated in transmission. The main source of infection is aspiration of contaminated water (Arch Intern Med 1986;146:1607).
  • Predisposing factors: Older age, smoking, COLD, alcoholism, and compromised hosts, especially transplant recipients. Patients with leukemia other than hairy cell leukemia and HIV infection are not at risk unless given steroids.
  • Clinical clues: Include temperature above 39°C, diarrhea, and neurologic symptoms, especially confusion. Laboratory clues include hyponatremia, elevated CPK, transaminase levels, and hematuria.
  • Species:L. pneumophila serogroup 1 is responsible for 90% of cases in the community. L. micdadei may cause multiple nodules on chest x-ray and can stain acid fast.

Diagnostic Tests:

Urinary antigen assay detects only L. pneumophila serogroup 1, but this accounts for 90% of cases acquired in the community, the test takes only 1–3 hours and reagents are available from two commercial sources. The test remains positive for months after infection and is not influenced by antibiotic treatment. This test is recommended by the authors for all patients hospitalized with CAP. Sputum culture requires selective media that is not widely used by most laboratories, requires 3–7 days for growth, and does not require the standard cytologic criteria of laboratories for sputum purulence as a contingency for culture (J Clin Microbiol 1994;32:209). DFA testing requires substantial microbiology expertise, sensitivity is relatively low, the test becomes negative after 4–6 days of antibiotic treatment, and specificity for L. pneumophila is nearly 100%. Serology shows seroconversion for IgM at 1–6 months and for IgG at 3–6 months; a single titer of 1:256 is presumptive evidence and a four-fold rise to 1:256 is probably more specific (CID 1995;20:1286). Serology of species other than L. pneumophila should be interpreted with caution. These observations are summarized in the Table 7.

TABLE 7
TABLE 7
  • Treatment: The recommendation is for drugs with good intrinsic activity vs. Legionella and good penetration into phagocytic cells. The preferred are clarithromycin, azithromycin and the newer fluoroquinolones. The duration of treatment is 10–14 days, except with azithromycin, which is 7–10 days and immunosuppressed patients who are usually treated for 21 days, or longer if there are persistent infiltrates on chest x-ray despite clinical response.
  • Prevention: Hospital water should be cultured and, if contaminated, should be disinfected with one of two methods: heating to 70–80°C followed by flushing of distal sites for 30 minutes (“super heat and flush”) or installation of copper-silver ionization units (Semin Respir Infect 1998;13:147).

Comment:

This article reviews some of the more controversial issues regarding Legionella and the infection it causes. The authors represent the group that did much of the original Legionella work in the 1976–1980 era led by Victor Yu from Pittsburgh who is clearly a noted authority in this field. Of particular interest are the following: 1) the conclusion that aspiration rather than inhalation is the major mechanism of infections; 2) L. pneumophila serogroup is responsible for 90% of cases (since many have suggested a rate of 50–70% which would make the urinary antigen assay much less sensitive); 3) the definition of the susceptible host which includes immunosuppressed hosts such as transplant recipients and steroid recipients, but not AIDS patients who also have compromised CMI; 4) the recommendation for routine cultures of hospital water as a method to control nosocomial acquisition (in disagreement with the CDC).

© 2002 Lippincott Williams & Wilkins, Inc.