대한흉부영상의학회 Korean Society of Thoracic Radiology

Discussion

Diagnosis With Brief Discussion

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Imaging Findings

Fig 1: Chest anteroposterior radiograph shows ill-defined opacity in medial aspect of right upper lobe.
Fig 2: Chest radiograph obtained two days later shows significant progression of right upper lobe lesion.
Fig 3 and 4: CT scans of the mediastinum and the lung window settings obtained at the same time as (2) shows
patchy area of consolidation in right upper lobe.

Past History

PI: The patient was admitted to our hospital for treatment of acute renal failure, diabetes melitus, atrial fibrillation with sick sinus syndrome, and hypertension.
The patient developed fever and cough on the sixtieth hospital day.

Figure 1: Initial radiograph
Figs. 2-4: Two days later.

Discussion

The most frequently isolated pathogens in nosocomial pneumonia are gram negative
and include P. aeruginosa, Enterobacter spp., K. pneumoniae, E. coli, Serratia marcescens, and Actinobacter spp.
Gram-positive pathogens, especially S. aureus, have also emerged as important causes of nosocomial pneumonia.

Although Legionella is less frequent cause of hospital-acquired pneumonia than these pathogens,
it is also considered an important nosocomial pathogen.
L. pneumophila may be responsible for up to 10% of nosocomial pneumonias and as much as 30% during endemic hospital outbreaks.

The spectrum of Legionella infection is not completely defined, however, and probably includes asymptomatic seroconversion,
mild self-resolving illness, Pontiac fever, Legionnaires' disease (LD), and isolated extrapulmonary infections.

Legionnaires' disease, febrile systemic illness with pneumonia, is acquired by inhaling aerosolized water containing Legionella organisms
or possibly by pulmonary aspiration of contaminated water.
Aerosols formed by contaminated water in plumbing systems and in cooling towers are the most common sources of infection.

Risk factors for acquisition of Legionnaires' disease include
corticosteroid administration, cytotoxcic chemotherapy, smoking, DM, age older than 50 years, AIDS,
immunosuppressive therapy for solid organ transplantation, chronic heart or lung disease, renal failure, and lung or hematologic cancer.

Especially, corticosteroid therapy, renal failure, and lung or hematologic malignancy have been reported as significant risk factors.
Therefore, our patient, a 59-year-old man, who had DM, renal failure, and heart disease was considered to be
at a high risk of infection with L. pneumophila.

LD does not have a characteristic radiographic appearance.
Seventy to 80% of patients present with diffuse patchy alveolar opacities or lobar/segmental consolidation.
Unilateral involvement ranges from 35% to 75%.
Ill-defined, rounded opacities are a frequent presentation and these opacities may progress to a lobar consolidation.
Cavitation may develop in areas of consolidation and
most cases of cavitation occur in immunocompromised patients or those with serious underlying disease.
Patients who have undergone organ transplantation have shown the highest frequency of cavitation in LD.

Pleural effusions are common, seen in 24% to 63% of cases.
These effusions are usually modest in extent and do not complicate treatment.
Hilar adenopathy and spontaneous pneumothorax can be seen as unusual manifestations.
There is a poor correlation between radiographic severity and prognosis.

Chest radiographic features of sporadic LD in nosocomial and community-acquired cases have been compared.
The case-fatality rate in nosocomial infection was 70%, compared to 22% for those that were community acquired.
It might be associated with higher number of patients with immunosuppression or severe underlying disease in nosocomial cases.
However, the radiographic appearance of these groups was quite similar.

The Legionella species are aerobic, fastidious, gram-negative bacilli that require cysteine for growth.
They do not stain well with ordinary Gram's stain, nor do they grow well on conventional culture media.
Therefore, the diagnosis of L. pneumophila is made by specific laboratory tests.

There are currently five primary laboratory tests available for the specific diagnosis of Legionella infection:
culture with special selective media, direct florescent antibody test (DFA), serologic tests, DNA probe, and urinary antigen test.

No laboratory test currently available is 100% accurate for the diagnosis of legionnaires' disease.
Thus empirical therapy must be considered in appropriate clinical settings.

The drug of choice for this disease is erythromycin.
Quinolone antimicrobials and azithromycin are more effective than erythromycin in experimental laboratory studies.
Thus these drugs are recommended as preferred agents for critically ill patients with LD.
With appropriate therapy, complete recovery occurs in approximately 80% to 90% of cases, particularly if there is no underlying illness.

Reference

1. Fairbank JT, Patel MM, Dietrich PA. Legionnaires' disease. J Thorac Imaging 1991;6:6-13.
2. Moore EH, Webb WR, Gamsu G, et al. Legionnaires' disease in the renal transplant patient: clinical presentation and radiographic progression. Radiology 1984;153:589-593
3. Helms CM, Viner JP, Weisenburger DD, et al. Sporadic Legionnaires' disease: clinical observations on 87 nosocomial and community-acquired cases. Am J Med Sci 1984;288:2-12.
4. Goetz MB, Finegold SM. Pyogenic bacterial pneumonia, lung abscess, and empyema. In: Murray JF, ed. Textbook of respiratory medicine. 3rd ed. Philadelphia: W.B. Saunders, 2000;985-1041.

Keywords

Lung, Infection, Bacterial infection,