Legionella

CASE 1

• A 65 year old man has fever and shortness of breath. His symptoms began 4 days ago with a "flu-like" illness consisting of low-grade fever, malaise, dry cough, headache, and joint pains. Two days ago, he went to a local clinic and was given a course of oral cefuroxime. However, his fever has continued to increase dramatically, and he is now having trouble breathing as well. He has also has some mild diarrhea.

• Ten days ago, he returned from a 2-week visit with his daughter, husband, and three grandchildren at their home in Manchester, England. He was unable to arrange a one-day return to Ghana from Manchester, so he spent one night in a hotel near Heathrow Airport. He ate a dinner and breakfast the next morning at the hotel, used the treadmill at the hotel gym, watched television briefly in the lobby, and shaved and took a hot shower in his room. The flight home was uneventful.

• The patient is an occasional cigarette smoker in spite of the fact that he has had several episodes of asthmatic bronchitis that required treatment with corticosteroids. He had his last course of steroids one week before his trip to England.

• On physical examination, the patient had a temperature of 39.6 degrees, heart rate of 105.min, and respirations of 28/min. There are crackles heard over the right middle lobe. A chest xray shows an infiltrate in this area (see below):

• Examination of sputum shows neutrophils but no predominant bacteria. The patient is treated with ciprofloxacin for "atypical pneumonias." Blood cultures are negative. The patient recovers slowly. however,

• Ten days later, the patient received a call from the health department at Heathrow informing him that 12 other clients of the airport hotel, all of whom were over age 55, fell ill during the same period of time that the patient stayed there. Mostof the ill clients had a urine antigen test positive for Legionella pneumophila serogroup 1; two had Legionella pneumophila serogroup 1 grown from their sputum on specialized media.

Questions:

1. Where did this patient acquire this infection? What did he do that most likely exposed him to these bacteria?
2. Where is Legionella found in nature? How does it grows in nature and how does it eventually get to humans?
3. Do patients become colonized in the upper respiratory tract with this organism before pneumonia occurs as they do with pneumococcus before pneumococcal pneumonia?
4. What is the fate of L. pneumophila when it gets into the pulmonary alveoli of a susceptible host?
5. How does L. pneumophila avoid being killed in macrophages?
6. This organism is susceptible to cefuroxime when tested in vitro. Why was this antibiotic not helpful in treating the infection?
7. What specific factors put this patient at risk for acquiring Legionnaires' disease?
8. Are his family members in Ghana at risk for acquiring this infection from him?

CASE 2

• On a single day in February, 52 of 143 workers on one assembly line at an automobile assembly plant took sick leave over a 2 day period. All complained of fever, malaise, joint pains, and mild cough. Those that saw a doctor had no specific physical findings, and those that had chest x-rays (25) had no abnormalities seen. None of the workers were hospitalized, and all of them returned to normal within 3 days or less of the onset of their illness. There were no secondary cases in the households of the ill workers. The plant was closed temporarily until the cause of the illness could be identified.

• An investigator from the health department reviewed the sequence of events at the plant and discovered that the ill workers were all clustered at one end of the assembly line. Suspecting Pontiac fever as a possible cause, she cultured the water from the automatic machine sprayers on the line (N.B. The sprayers were designed to keep the assembly machinery from overheating.) L. pneumophila serogroup 1 was isolated from one water sprayer located centrally among the work sites of the ill workers, but none of the other sprayers in the building were positive.

• The water sprayers were all disinfected, and the plant was reopened. No further cases occurred. Six weeks after the outbreak, 20 previously ill workers who had blood samples taken at the time of the illness had repeat sampling done. Eighteen had developed antibodies against L. pneumophila serogroup 1, confirming that the outbreak was due to Pontiac fever.

Questions:

1. How is the illness in this outbreak different from that of case 1? Is this Pontiac fever infection? Was an antibiotic necessary?
2. The ill workers in this outbreak had none of the risk factors for Legionnaires' disease? What does this suggest?
3. Are the organisms that cause Pontiac fever the same as those that cause Legionnaires' disease?
4. How many serogroups of L. pneumophila are there? How many other species are there in the genus Legionella, and do any of them cause disease?