Legionella pneumonia.

VOL 47: SEPTEMBER • SEPTEMBRE 2001❖Canadian Family Physician•Le Médecin de famille canadien 1737

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Just the Berries

Lesley Ruggles, MD

Legionella pneumonia

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Although a common cause of severe pneumonia (after Streptococcus pneumoniae and Chlamydia pneumoniae) requiring admission to an intensive care unit, it is, in fact, a much rarer cause of “walk- ing” pneumonia.¹ The disease was first described during the infamous American Legion convention outbreak in Philadelphia, Pa. Interestingly, it is rare in Europe.

Most of the information for this ar ticle was derived from the most recent editions of standard infectious disease texts.^1,2This information was sup- plemented by a MEDLINE search (via MDConsult) for articles listed under “Legionella pneumonia.”

Legionella pneumophilia causes two distinct syndromes: Legionnaires disease and Pontiac fever.² Legionnaires disease has a 2- to 10-day incubation period during which patients develop fever, headache, malaise, and myalgias and then pneumonia. Many patients have severe chest pain and 25% to 50% have watery diarrhea. Some also have nausea, vomiting, abdominal pain, and renal and central ner vous system manifestations.

Pontiac fever, an acute self-limited influenzalike ill- ness without pneumo-

nia, typically has an incubation period of only 24 to 48 hours, and patients recover in a week.

Misconceptions Although we tend to associate Legionella pneumonia with out- breaks, in fact more than 80% of cases are

sporadic. Despite this, Nova Scotia Public Health follows up with patients if results of culture or antibody tests are positive. The organism is found in water and proliferates under favourable conditions (generally, a suitable temperature, sediment to which to adhere, and symbiotic microorganisms for growth). This is ironic con- sidering that the bacterium is fastidious and diffi- cult to culture in the laborator y. Various strains appear to have var ying virulence; some release numerous toxins, but the toxins are not necessar- ily linked to virulence.

The lungs’ main defence against Legionella pneumonia is mucociliar y clearance of the bac- terium. Conditions, such as cigarette smoking, chronic obstructive lung disease, and alcoholism, that hinder this clearance render patients suscep- tible to the disease. Immunocompromised patients, including transplant recipients, patients with HIV infection, and those receiving steroids, are also at risk.

Clinically, little differentiates Legionella from other atypical organisms.³ Up to 50% of patients have diarrhea or gastrointestinal symptoms, and even more patients have headaches. Laborator y test results are similar to those for other pneumo- nias, except for a propensity toward low serum sodium levels (Na < 130). Gram stain of sputum or fluid reveals many polymor- phonucleotides but few or no organisms (small, faint pleomor- phic Gram-negative rods easily obscured by nor mal sputum flora). Chest x-ray

“Just the Berries” for Family Physicians originated at St Martha’s Regional Hospital in 1991 as a newsletter for members of the Department of Family Medicine. Its purpose was to provide useful, practical, and current informa- tion to busy family physicians. It is now distributed by the Medical Society of Nova Scotia to all family physicians in Nova Scotia. Topics discussed are suggested by family physicians and, in many cases, articles are researched and written by family physicians.

Just the Berries has been available on the Internet for several years. You can find it at www.theberries.ns.ca.Visit the site and browse the Archives and the Berries of the Week. We are always looking for articles on topics of interest to family physicians. If you are interested in contributing an arti- cle, contact us through the site. Articles should be short (350 to 1200 words), must be referenced, and must include levels of evidence and the resources searched for the data. All articles will be peer reviewed before publication.

Dr Ruggles practises family medicine at St Martha’s Regional Hospital in Antigonish, NS.

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results are usually abnormal by the third day, typically with a segmental infiltrate. These infections often become multilobar, and widespread involvement is common even after initiation of appropriate antibiotic treatment. Radiographic clearance takes 1 to 4 months.

Specific testing for Legionella pneumophilia can be done in a spe- cial culture medium or by direct flu- orescent antibody testing (DFA) of sputum or urine. Because a large number of organisms need to be pre- sent, DFA is less sensitive than cul- ture; a positive result on chest x-ray film is more likely with a multilobar infiltrate. A four-fold rise in acute and convalescent immunoglobulin G titres is also diagnostic, although the lag time to receiving results makes this impractical as a clinically useful test.

Treatment

Treatment requires antibiotics with high intracellular concentrations.

Because Legionella typically causes severe disease often with gastroin- testinal involvement, parenteral treatment is recommended. The organism is sensitive to macrolides, quinolones, and rifampin. Azithro- mycin, at a dose of 1 g followed by 500 mg ever y 24 h, has replaced er ythromycin as first-line treat- ment; intravenous administration of

erythromycin can irritate veins and r equir es large fluid volumes to infuse. Intravenous ciprofloxin or levofloxin ar e alter natives. For severe disease, most texts (level 4 evidence) r ecommend an intra- venous macrolide in combination with oral rifampin. T wo weeks’

treatment is recommended for mild disease; 3 weeks for severe disease or for immunocompr omised patients. An article in a recent issue of M e d i c a l C l i n i c s o f N o r t h America,⁴discussing antibiotic ther- apy and resistance, has suggested that quinolones should be first-line therapy for Legionella infection because they achieve such high intracellular concentrations. To date, antibiotic resistance has not been a problem in organisms caus- ing atypical pneumonia.⁴

Legionella pneumophilia is acquired through inhalation of aerosolized water. During outbreaks, health workers tr y to identify the common water source that has caused the disease. Superheating the water (to 70°C) and flushing the source is necessar y to eradicate Legionella. Because the bacteria are chlorine tolerant, hyperchlorination is a less effective strategy for decon- taminating water sources.

Because Legionella is a common cause of severe community-acquired pneumonias and our first-line agents

for these pneumonias are macro- lides and quinolones, routine testing seems unnecessar y. Per haps in severe cases, especially those involving patients with multilobar infiltrates and markers of atypical disease (gastrointestinal symptoms, normal white blood cell counts, or low serum sodium concentrations), it would be pr udent to test for Legionella. When patients are criti- cally ill, specific diagnoses are often helpful. They guide treatment plans, and knowing the natural histor y of the disease can aid in predicting a par ticular patient’s course and outcome.

Acknowledgment

I thank Dr Scott Rappard, Respirologist at St Martha’s Regional Hospital in Antigonish, NS, for reviewing the draft copy of this arti- cle.

References

1. Mandell LA. Principles and practice of infectious diseases.

5th ed. London, Engl: Churchill Livingstone Inc; 2000.

p. 2424-35.

2. American Academy of Pediatrics. Red book 2000. Report of the Committee on Infectious Diseases. 25th ed.

Washington, DC: American Academy of Pediatrics;

2000. p. 364-5.

3. Sopena N, Sabria-Leal M, Pedro-Botet ML, Padilla E, Dominguez J, Morera J, et al. Comparative study of the clinical presentation of Legionella pneumonia and other community-acquired pneumonias. Chest

1998;113(5):1195-200.

4. Cunha BA. Antibiotic resistance. Med Clin North Am 2000;84(6):1407-29.

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VOL 47: SEPTEMBER • SEPTEMBRE 2001❖Canadian Family Physician•Le Médecin de famille canadien 1739