LEGIONNAIRES DISEASE

Legionnaires’ Disease

The incidence of legionnaires’ disease (LD) seems to increase with age, particularly in males [36]. It was considered an infrequent cause of pneumonia in the past, but it currently ranks second to pneumococcus in the list of etiologic agents of severe community-acquired pneumonia (CAP) of bacterial origin [2, 24, 60, 89]. Considering less severe cases, in a series of 145 pneumonias in which BCYE culture, serology and the Legionella urinary antigen (LUA) test were systematically applied, Vergis et al. [91] reported a prevalence of LD of 13.7%. In another series of 392 adult patients with CAP treated in a university hospital, Sopena et al. found a prevalence of 12.5%, and LD was the second cause of pneumonia [83].

13 – Antibiotic therapy of community-acquired pneumonia (CAP) caused by atypical agents

Macrolides, fluoroquinolones, doxycycline, and ketolides show a good intrinsic activity against intracellular pathogens which are responsible for a variable percentage of community-acquired pneumonia (CAP). These therapeutic agents all seem effective in treating most cases of CAP caused by Mycoplasma pneumoniae, Chlamydia pneumoniae, or Legionella spp. Among quinolones, the more recent fluoroquinolones, such as gemifloxacin or moxifloxacin, generally show a better intrinsic activity than the older ones. Among macrolides, azithromycin, and clarithromycin show a better pharmacokinetic profile. Both of them are available in intravenous form. It is quite common for M. pneumoniae and C. pneumoniae to continue to be shed in respiratory secretions, weeks after an effective therapy. The clinical relevance of this finding is not clear since most of these patients have a good outcome. Azithromycin, due to its advantageous pharmacokinetic profile, seems the best option when antibiotic prophylaxis is considered in some epidemiological settings. It has been proved effective in closed M. pneumoniae outbreaks.

Excellent activity of newer quinolones on Legionella pneumophila in J774 macrophages

The activity of six antibiotics directed against intracellularly multiplying Legionella pneumophilia was examined in tissue cultures with J774 macrophages. The drugs tested were the new quinolones, BAY Y 3118 and clinafloxacin, and ciprofloxacin, erythromycin, gentamicin and ampicillin served as reference drugs. Additionally, the MICs of these drugs against L. pneumophila were determined in vitro by broth microdilution. Despite their low MIC values, ampicillin and gentamicin did not inhibit intracellular multiplication of L. pneumophila in J774 macrophages. In contrast, an inhibition of intracellular growth could be demonstrated for the four other antibiotics. The new quinolones BAY Y 3118 and clinafloxacin showed the highest activity against intracellular L. pneumophila. At a concentration of 0.00078 mg/L already, a marked reduction in bacterial counts was seen for both drugs in comparison to the growth control without antibiotics. The corresponding effective concentrations were 0.0125 mg/L for ciprofloxacin and 0.2 mg/L for erythromycin. It may be concluded that new quinolone derivatives might become an alternative to erythromycin and rifampicin which at present are the drugs of primary choice for the treatment of legionnaires' disease.

Natural resistance to infection with Legionella pneumophila: chromosomal localization of the Lgn1 susceptibility gene

Legionella pneumophila is a strict intracellular pathogen that replicates in the professional phagocytes of the human and guinea pig host. Although murine macrophages from most inbred strains are non-permissive to intracellular replication of L. pneumophila, inflammatory macrophages from the mouse strain A/J are completely permissive to intracellular replication of this bacterium. This genetic difference is controlled by the expression of a single autosomal gene designated Lgn1, with non-permissiveness behaving as completely dominant over permissiveness. We have used a total of 25 AXB/BXA recombinant inbred mouse strains and 182 (A/J x C57BL/6J) x A/J segregating backcross progeny (A/J, permissive; C57BL/6J, non-permissive) to map the Lgn1 gene. Animals were individually typed for tolerance to intracellular replication by in vitro infection of their inflammatory macrophages with L. pneumophila. All animals segregated into two nonoverlapping groups. Examination of the strain distribution pattern of the AXB/BXA strains for Lgn1 initially identified linkage to Chromosome (Chr) 13 markers. Genotyping of the 25 AXB/BXA strains and the 182 backcross progeny for 11 Chr 13 markers established that Lgn1 mapped to Chr 13, with the gene order and intergene distance D13Mit231-(5.5 +/- 1.5)-D13Mit193-(2.2 +/- 0.9)-D13Mit194- (1.1 +/- 0.6)-D13Mit128-(2.6 +/- 1.0)-Lgn1-(2.2 +/- 0.9)-D13Mit70-(3.9 +/- 1.3)- D13Mit73-(7.2 +/- 1.7)-D13Mit53-(0.7 +/- 0.5)-D13Mit32-(0.7 +/- 0.5)-D13Mit77- (0.7 +/- 0.5)-D13Mit78. This portion of Chr 13 is homologous to the distal portion of human Chr 5, 5q11-5q13, suggesting a possible location of a human LGN1 homolog. Understanding the molecular basis of the high permissiveness of A/J macrophage to L. pneumophila may shed light on the survival strategy of this bacterium in highly permissive human phagocytes. This may be achieved by positional cloning of Lgn1, and the identification of the Lgn1 subchromosomal region reported here is a first step towards that goal.

Intensive care aspects of severe Legionella pneumonia

A case of extensive Legionella pneumonia is presented. The patient required an extended period of artificial ventilation, notably punctuated by episodes of dysrhythmia and severe haemodynamic instability, but who nevertheless eventually recovered. Intensive care aspects of Legionnaires' disease are discussed.