Thrombocytopenia and platelet microvesicle formation caused by Legionella pneumophila infection

Legionella Pneumophila Presenting as a Rare Cause of Acute Thrombocytopenia: A Case Report and Review of Literature

Introduction

Legionella pneumophila can cause a wide spectrum of clinical manifestations, ranging from a mild flu-like illness to fulminant multi-organ involvement, characterised by severe pneumonia, diarrhoea, encephalopathy, shock, hepatic dysfunction and renal failure. Very rarely, it can be associated with haematologic conditions such as thrombotic thrombocytopenic purpura (TTP), haemolytic uraemic syndrome (HUS) and immune thrombocytopenic purpura (ITP). We report a rare case of L. pneumophila causing ITP and review previously published cases of thrombocytopenia associated with Legionellosis in the literature.

Case description

A 53-year-old male presented with fevers, chills, a productive cough and severe haemoptysis. Blood work was remarkable for leukocytosis, severe thrombocytopenia and hyponatraemia. Computed tomography (CT) imaging showed left lower lobe lung consolidation, and a peripheral blood smear showed giant platelets consistent with ITP. Legionella urine antigen testing returned positive. He was treated with intravenous immunoglobin, steroid taper and a ten-day course of azithromycin, which led to normalisation of his platelet count and resolution of the pneumonia.

Discussion

L. pneumophila can lead to complement-mediated destruction of platelets resulting in ITP. Antibodies against L. pneumophila can also cross-react with the enzyme ADAMTS13, inhibiting its function and resulting in TTP and HUS. Additionally, L. pneumophila can infect vascular endothelial cells causing their death and stimulating release of von Willebrand factor (vWF) multimers into the bloodstream, promoting thrombosis and platelet consumption.

Conclusion

It is important for internists to consider L. pneumophila in the differential for any patient presenting with pneumonia and severe thrombocytopenia. Earlier detection and intervention can lead to prevention of critical bleeding and better outcomes.

LEARNING POINTS

Legionella pneumophila is rarely associated with different haematologic disorders resulting in severe bleeding diathesis as well as thrombosis.It is important for internists to consider Legionella pneumophila in the differential diagnosis for any patient presenting with pneumonia and severe thrombocytopenia.Earlier detection and intervention can lead to prevention of critical bleeding and better outcomes.

Incidence and risk factors associated with progression to severe pneumonia among adults with non-severe Legionella pneumonia

BACKGROUND

Legionella species are important causative organisms of severe pneumonia. However, data are limited on predictors of progression to severe Legionella pneumonia (LP). Therefore, the risk factors for LP progression from non-severe to the severe form were investigated in the present study.

METHODS

This was a retrospective cohort study that included adult LP patients admitted to a 2,700-bed referral center between January 2005 and December 2019.

RESULTS

A total of 155 patients were identified during the study period; 58 patients (37.4%) initially presented with severe pneumonia and 97 (62.6%) patients with non-severe pneumonia. Among the 97 patients, 28 (28.9%) developed severe pneumonia during hospitalization and 69 patients (71.1%) recovered without progression to severe pneumonia. Multivariate logistic regression analysis showed platelet count ≤150,000/mm3 (odds ratio [OR], 2.923; 95% confidence interval [CI], 1.100-8.105; P=0.034) and delayed antibiotic treatment >1 day (OR, 3.092; 95% CI, 1.167-8.727; P=0.026) were significant independent factors associated with progression to severe pneumonia.

CONCLUSIONS

A low platelet count and delayed antibiotic treatment were significantly associated with the progression of non-severe LP to severe LP.

Immune thrombocytopenic purpura and legionella infection: A case report highlighting the association

Immune thrombocytopenic purpura (ITP) can be acquired or secondary to other drugs, infections, or autoimmune disorders. Legionella is a known intracellular organism that causes Legionnaire's disease and affects the lungs. Presented is the first case showing a direct association between Legionella and ITP. Our patient was a 61-year-old female with a past medical history of asthma whose clinical presentation was consistent with pneumonia secondary to Legionella. Her hospital course was complicated by critical bleeding with severe thrombocytopenia. She responded to antibiotics, steroids, and intravenous immunoglobulins (IVIG). Our case suggests an association between ITP and Legionella and emphasizes its timely diagnosis for appropriate treatment.

Microvesicles at the crossroads between infection and cardiovascular diseases

Observational and experimental studies continue to support the association of infection and infection-stimulated inflammation with development of cardiovascular disease (CVD) including atherosclerosis and thrombosis. Microvesicles (MV) are heterogeneous populations of sealed membrane-derived vesicles shed into circulation by activated mammalian cells and/or pathogenic microbes that may represent an interface between bacterial/microbial infection and increased risk of CVD. This review evaluates how MV act to modulate and intersect immunological and inflammatory responses to infection with particular attention to progression of CVD. Although infection-related stimuli provoke release of MV from blood and vascular cells, MV express phosphatidylserine and other procoagulant factors on their surface, which initiate and amplify blood coagulation. In addition, MV mediate cell-cell adhesion, which may stimulate production of pro-inflammatory cytokines in vascular cells, which in turn aggravate progression of CVD and propagate atherothrombosis. MV transfer membrane receptors, RNA and proteins among cells, and present auto-antigens from their cells of origin to proximal or remote target cells. Because MV harbor cell surface proteins and contain cytoplasmic components of the parent cell, they mediate biological messages and play a pivotal role in the crossroad between infection-stimulated inflammation and CVDs.

Comparisons of clinical characters in patients with pneumococcal and Legionella pneumonia

BACKGROUND/PURPOSE

The etiology of pneumonia is usually unknown, but the availability of urinary pneumococcal and Legionella antigen tests can improve the diagnostic yield. Our aim was to provide clinical clues to help clinicians perform the appropriate urinary antigen tests.

METHODS

A retrospective study of patients admitted to the National Cheng Kung University Hospital between July 2006 and June 2008 was conducted. Patients aged over 18 years presenting with clinical symptoms and signs, radiological findings compatible with pneumonia, and a positive pneumococcal or Legionella pneumophila urinary antigen test, were included. Medical records were reviewed for data collection.

RESULTS

Overall, 55 adults with pneumonia, including 42 with pneumococcal pneumonia (PP) and 13 with Legionella pneumonia (LP), were enrolled. On admission, patients with PP tended to be older (73.5 years vs. 59.1 years; p=0.001), had lower body weights (52.0 kg vs. 69.7 kg; p < 0.001), more frequent respiratory symptoms (59.5%vs. 0%; p < 0.001), and lower systolic (123.0 mmHg vs. 141.0 mmHg; p=0.004) and diastolic blood pressures (68.3 mmHg vs. 81.7 mmHg; p=0.008), compared with patients with LP. However, those with LP had higher body temperatures (39.0°C vs. 37.5°C; p < 0.001), a higher incidence of relative bradycardia (45.5%vs. 0%; p < 0.001), diarrhea (15.4%vs. 0%; p= 0.053), and lower platelet counts (178.5 × 10(3)/mm(3)vs. 233.7 × 10(3)/mm(3); p= 0.026). Radiological findings showed that the major abnormality, lobar consolidation, was indistinguishable between LP and PP. The percentage of patients requiring intensive care (35.7%vs. 38.5%) or ventilator support (31%vs. 23.1%) and in-hospital crude mortality rates (9.5%vs. 7.7%) was similar in both groups.

CONCLUSION

Some clinical and laboratory characteristics may be regarded as important clues indicating the need for an appropriate urinary antigen test in patients with pneumonia.

A bacterial ecto-triphosphate diphosphohydrolase similar to human CD39 is essential for intracellular multiplication of Legionella pneumophila

As part of its pathogenesis, Legionella pneumophila persists within human alveolar macrophages in non-acidified organelles that do not mature into phagolysosomes. Two L. pneumophila genes, lpg0971 and lpg1905, are predicted to encode ecto-nucleoside triphosphate diphosphohydrolases (ecto-NTPDases) that share sequence similarity with human CD39/NTPDase1. The predicted products possess five apyrase conserved domains that are typical of eukaryotic ecto-NTPDases. In this study, we found that an lpg1905 mutant was recovered in lower numbers from macrophages, alveolar epithelial cells and the amoeba, Hartmannella vermiformis compared with wild-type L. pneumophila and an lpg0971 mutant. Similar to human CD39, recombinant purified Lpg1905 exhibited ATPase and ADPase activity and possessed the ability to inhibit platelet aggregation. Mutation of a conserved Glu159 residue that is essential for CD39 activity inhibited ATPase and ADPase activity of Lpg1905. In addition, enzyme activity was inhibited in the presence of the specific ecto-NTPDase inhibitor, ARL67156. The entry and replication defect of the lpg1905 mutant was reversed upon transcomplementation with lpg1905 but not lpg1905E159A encoding an enzymatically inactive form of the protein. Although several protozoan parasites exhibit ecto-NTPDase activity, including Toxoplasma gondii, Trichomonas vaginalis and Trypanosoma cruzi, this is the first time a bacterial ecto-NTPDase has been implicated in virulence.