Hypophosphatemia: diagnostic significance in Legionnaires' disease

A Case of Legionella pneumophila Serogroup 13 Pneumonia Based on the Detection of Serogroup-Specific Genes in Culture-Negative Sputum

Legionella pneumophila serogroup (SG) 1, the main cause of Legionnaires' disease, can be diagnosed using urinary antigen testing kits. However, lower respiratory tract specimen cultures are required to identify L. pneumophila SG 2-15. We attempted to detect L. pneumophila SG-specific genes in a culture-negative sputum specimen from a patient with pneumonia who was suspected to have Legionnaires' disease. Two multiplex PCR methods targeting L. pneumophila were modified and amplicons considered to be SG13 specific were detected. Direct sequencing revealed that the amplicons were identical to the nucleotide sequence of L. pneumophila SG13. Based on the presentation and clinical course (fever, muscle pain, disturbance of consciousness, high C-reactive protein titer, rhabdomyolysis, hypophosphatemia, and symptomatic improvement with levofloxacin treatment), in combination with the detection of L. pneumophila SG-specific genes, we suspected L. pneumophila SG13 pneumonia. L. pneumophila non-SG1 pneumonia is thought to be underestimated because of its difficult laboratory diagnosis. The modified multiplex PCR system for lower respiratory tract specimens revealed in this study is likely to improve the diagnosis of Legionnaires' disease caused by L. pneumophila SG13 and other SGs.

Legionella: An uncommon cause of community-acquired pneumonia

ABSTRACT

Legionnaires disease is an important, relatively uncommon, yet well known form of atypical community-acquired pneumonia (CAP). If not appropriately treated in the early stage of infection, it can be fatal. Several factors increase the risk of contracting Legionnaires disease, including age over 50 years, chronic cardiovascular disease, underlying respiratory disease, chronic renal disease, diabetes, smoking, any immunosuppressing condition, travel history, and certain types of employment. Legionnaires disease can present without the usual symptoms associated with pneumonia. The incidence of Legionnaires disease is increasing, and because of its morbidity and mortality, clinicians should consider it in the differential when treating patients with CAP. This article reviews the pathophysiology and treatment of Legionnaires disease and when to refer patients to tertiary centers for higher levels of care, including extracorporeal membrane oxygenation.

Significance of Hypophosphatemia in Patients with Pneumonia

Objective Phosphate is a fundamental element involved in a number of physiological pathways. A previous study showed abnormal laboratory findings and a higher mortality in hypophosphatemic patients than in normophosphatemic patients with pneumonia. Sporadic cases of pneumonia due to Legionella spp., Streptococcus pneumoniae, and viruses have been reported; however, the significance of hypophosphatemia in patients with pneumonia has not been adequately studied. We determined whether or not hypophosphatemia in patients with community-acquired pneumonia (CAP) was associated with specific pathogens, patient factors, disease severity, and mortality. Method We retrospectively analyzed 600 patients with CAP who were admitted to our hospital between January 1, 2010, and December 31, 2019. Results Hypophosphatemia was found in 72 (12.0%) of the 600 patients. The most frequent causative microbial agents of CAP in patients with hypophosphatemia were S. pneumoniae, Legionella spp., and influenza virus, whereas in severely ill patients with hypophosphatemia, influenza virus was the most common. Legionella spp., diabetes mellitus, and severe pneumonia were the independent factors for hypophosphatemia in the multivariable analysis. An impaired performance status, severe status on admission, interstitial pneumonia, bacteremia, and guideline-discordant therapy were the independent factors associated with mortality in the multivariable analysis. Hypophosphatemia was not significantly associated with mortality but showed a trend towards higher mortality in the multivariable analysis. Conclusion Hypophosphatemia was not associated with the prognosis in patients with CAP. However, the significance of hypophosphatemia for clinicians lies in the laboratory findings that predict abnormal glucose metabolism, Legionella infection, and severe disease.

Lower serum phosphate levels in patients with Legionella pneumonia relative to patients with non-Legionella pneumonia

INTRODUCTION

Few studies have evaluated serum phosphate levels in patients with Legionella pneumonia admitted to hospitals in Japan. This study aimed to assess serum phosphate levels among inpatients with Legionella pneumonia on admission and compare them to those of inpatients with non-Legionella community-acquired pneumonia.

METHODS

This case-control study included patients aged ≥16 years who were treated for Legionella pneumonia from April 2011 through March 2017 and those aged ≥16 years who were treated for non-Legionella community-acquired pneumonia from August 2014 through July 2015. Legionella pneumonia was diagnosed based on a positive result on the urinary antigen test, as well as radiographic examinations. Serum phosphate levels on admission were compared between Legionella and non-Legionella patients. In addition, serum phosphate levels on admission and on hospital day 5-7 were compared in Legionella patients.

RESULTS

We evaluated 8 Legionella patients and 61 non-Legionella patients. Median serum phosphate levels on admission were 1.90 and 2.80 mg/dL in Legionella and non-Legionella patients, respectively (P = 0.008). By hospital day 5-7, serum phosphate levels in Legionella patients had increased to 2.61 mg/dL (P = 0.029, relative to admission), which did not significantly differ from those of non-Legionella patients on admission (P = 0.372).

CONCLUSION

Serum phosphate levels on admission were approximately 32% lower in Legionella pneumonia patients compared to non-Legionella pneumonia patients, but both were comparable by hospital day 7.

Legionnaire's Disease: A Clinical Diagnostic Approach

Legionnaire's disease is a nonzoonotic atypical pneumonia caused by Legionella sp that occurs sporadically or in outbreaks. Legionnaire's disease pneumonia is accompanied by several extrapulmonary clinical and laboratory findings. Rather than testing all pneumonias for Legionnaire's disease, the clinical challenge is to recognize the diagnostic significance of Legionnaire's disease's. The pretest probability of Legionnaire's disease is increased if several characteristic extrapulmonary findings are present. Similarly, if certain key findings are absent, Legionnaire's disease may be eliminated from further diagnostic consideration. If characteristic clinical findings are present, then specific tests should be ordered to confirm or rule out Legionnaire's disease.

Legionnaire's Disease and its Mimics: A Clinical Perspective

Whenever the cardinal manifestations of a disorder occur in similar disorders, there is potential for a disease mimic. Legionnaire's disease has protean manifestations and has the potential to mimic or be mimicked by other community acquired pneumonias (CAPs). In CAPs caused by other than Legionella species, the more characteristic features in common with legionnaire's disease the more difficult the diagnostic conundrum. In hospitalized adults with CAP, legionnaire's disease may mimic influenza or other viral pneumonias. Of the bacterial causes of CAP, psittacosis and Q fever, but not tularemia, are frequent mimics of legionnaire's disease.

Diagnostic dilemma: Epstein-Barr virus (EBV) infectious mononucleosis with lung involvement or co-infection with Legionnaire's disease?

BACKGROUND

Hospitalized adults with fever and "pneumonia" can be a difficult diagnostic challenge particularly when the clinical findings may be due to different infectious diseases.

METHODS

We recently had an elderly female who presented with fever, fatigue and dry cough with elevated serum transaminases and lung infiltrates. The diagnosis of Epstein-Barr virus (EBV) infectious mononucleosis (IM) was made based on a positive Monospot test, elevated EBV VCA IgM titer, and highly elevated EBV viral load. Her chest infiltrates were not accompanied by hilar adenopathy which may occur with EBV IM. Her dry cough persisted and she developed abdominal pain.

RESULTS

Legionnaire's disease was considered because she had extra-pulmonary findings characteristic of Legionnaire's disease, e.g., relative bradycardia, abdominal pain, hyponatremia, hypophosphatemia, elevated ferritin levels, microscopic hematuria. Legionella titers were negative, but Legionella (serogroup 1) urinary antigen was positive.

CONCLUSIONS

We present a diagnostic dilemma in an elderly female with both Legionnaire's disease and Epstein-Barr virus infectious mononucleosis with pulmonary involvement.

Adult human metapneumonovirus (hMPV) pneumonia mimicking Legionnaire's disease

In adults hospitalized with viral pneumonias the main differential diagnostic consideration is influenza pneumonia. The respiratory viruses causing viral influenza like illnesses (ILIs), e.g., RSV may closely resemble influenza. Rarely, extrapulmonary findings of some ILIs may resemble Legionnaire's disease (LD), e.g., adenovirus, human parainfluenza virus (HPIV-3). We present a most unusual case of human metapneumonovirus pneumonia (hMPV) with some characteristic extrapulmonary findings characteristic of LD, e.g., relative bradycardia, as well as mildly elevated serum transaminases and hyphosphatemia. We believe this is the first reported case of hMPV pneumonia in a hospitalized adult that had some features of LD.

Treatment of hypophosphatemia in the intensive care unit: a review

Introduction

Currently no evidence-based guideline exists for the approach to hypophosphatemia in critically ill patients.

Methods

We performed a narrative review of the medical literature to identify the incidence, symptoms, and treatment of hypophosphatemia in critically ill patients. Specifically, we searched for answers to the questions whether correction of hypophosphatemia is associated with improved outcome, and whether a certain treatment strategy is superior.

Results

Incidence: hypophosphatemia is frequently encountered in the intensive care unit; and critically ill patients are at increased risk for developing hypophosphatemia due to the presence of multiple causal factors. Symptoms: hypophosphatemia may lead to a multitude of symptoms, including cardiac and respiratory failure. Treatment: hypophosphatemia is generally corrected when it is symptomatic or severe. However, although multiple studies confirm the efficacy and safety of intravenous phosphate administration, it remains uncertain when and how to correct hypophosphatemia. Outcome: in some studies, hypophosphatemia was associated with higher mortality; a paucity of randomized controlled evidence exists for whether correction of hypophosphatemia improves the outcome in critically ill patients.

Conclusions

Additional studies addressing the current approach to hypophosphatemia in critically ill patients are required. Studies should focus on the association between hypophosphatemia and morbidity and/or mortality, as well as the effect of correction of this electrolyte disorder.

Severe Q fever community-acquired pneumonia (CAP) mimicking Legionnaires' disease: Clinical significance of cold agglutinins, anti-smooth muscle antibodies and thrombocytosis

Atypical community-acquired pneumonia (CAP) may be caused by zoonotic or nonpulmonary pathogens. However, atypical pathogens are systemic infectious disease accompanied by pneumonia in contrast with typical bacterial pathogens with infection limited to the lungs and absent extrapulmonary findings. Clinically and radiologically, the atypical CAP pathogens that most closely resemble each other are psittacosis, Q fever, and Legionnaires' disease. Psittacosis can usually be readily suspected or eliminated on the basis of a recent psittacine bird contact history. The 2 atypical pneumonias that most closely resemble each other clinically are Q fever and Legionnaires' disease. The epidemiology of Q fever is related to livestock, and sporadic cases are related to contact to parturient cats. In nonendemic areas, Q fever CAP mimics Legionnaires' disease most closely. Both Q fever and Legionella CAP have several clinical and laboratory features in common. However, there are subtle but important differences that allow the astute clinician to differentiate between these 2 disorders on the basis of clinical and nonspecific laboratory findings before definitive diagnostic tests results are reported. We report a case of severe Q fever CAP mimicking Legionnaires' disease in a young adult normal host. Her initial zoonotic contact history was negative, and her clinical presentation suggested Legionnaires' disease as the most likely diagnosis. Against the diagnosis of Legionnaires' disease was the patient's age and occurrence of the disease in spring time. In contrast, Legionnaires' disease is usually an infection of older individuals and occurs in late summer/fall. Although the patient did not have splenomegaly, a common finding in Q fever CAP, she did have mild hepatomegaly. Hepatomegaly is a uncommon in Q fever CAP but is not a feature of Legionnaires' disease. In the absence of a positive zoonotic contact history, the cardinal findings pointing to the diagnosis of Q fever in this case were "multiple round opacities" on chest computed tomography scan and thrombocytosis during her hospitalization. Against the diagnosis of Legionnaires' disease was the absence of hypophosphatemia and highly elevated ferritin levels. In patients with atypical pneumonias in whom the clinical presentation and nonspecific laboratory findings suggest Legionnaires' disease, but in addition have findings not associated with Legionnaires' (eg, hepatomegaly, thrombocytosis), Q fever serology should be ordered. We conclude that Q fever may closely mimic Legionnaires' disease. Severe atypical CAP with "multiple round opacities" on chest x-ray/computed tomography chest scan with elevated anti-smooth muscle antibodies or thrombocytosis should suggest the diagnosis of Q fever and prompt specific testing for Q fever. Rarely, Q fever CAP may be associated with elevated cold agglutinin titers.

Atypical pneumonias: current clinical concepts focusing on Legionnaires' disease

PURPOSE OF REVIEW

This review provides clinicians with an overview of the clinical features of the atypical pneumonias. Atypical community-acquired pneumonia pathogens cause systemic infections with pneumonia. The key to the clinical diagnosis of atypical pneumonias depends on recognizing the characteristic pattern of extrapulmonary organ involvement different for each pathogen. As Legionella is likely to present as severe pneumonia and does not respond to beta-lactams, it is important to presumptively diagnose Legionnaires' disease clinically so that Legionella coverage is included in empiric therapy. This study reviews the clinical features and nonspecific laboratory markers of atypical pathogens, focusing on Legionnaires' disease.

RECENT FINDINGS

Case reports/outbreaks increase our understanding of Legionnaires' disease transmission. Both Mycoplasma pneumoniae and Chlamydophilia pneumoniae may cause asthma. Antimicrobial therapy of Chlamydophilia pneumoniae/Mycoplasma pneumoniae is important to decrease person-to-person spread and to decrease potential long-term sequelae.

SUMMARY

Atypical pulmonary pathogens cause systemic infections accompanied by a variety of characteristic extrapulmonary features. Clinically, it is possible to differentiate Legionnaires' disease from the other typical/atypical pneumonias. Rapid clinical diagnosis of atypical pathogens, particularly Legionnaires' disease, is important in selecting effective empiric therapy and prompting definitive laboratory testing.

Legionella community-acquired pneumonia (CAP) presenting with spontaneous bilateral pneumothoraces

Legionnaires' disease is a common cause of non-zoonotic atypical community-acquired pneumonia (CAP). Legionnaires' disease has varied manifestations but may be diagnosed clinically on the basis of its characteristic pattern of extra-organ involvement. In a patient with non-zoonotic CAP, the clinical and laboratory features in a patient with CAP pointing to the diagnosis of Legionnaires' disease include relative bradycardia, mental confusion/ encephalopathy, loose stools/diarrhea, abdominal pain, mild/transient increases in serum transaminases, decreased serum phosphorous, a highly elevated C-reactive protein (CRP), elevated creatinine phosphokinase (CPK), highly elevated serum ferritin levels, or microscopic hematuria. The radiologic manifestations of Legionnaires' disease are varied and no radiographic appearance is pathopneumonic. Patchy infiltrates in Legionnaires' disease are symmetrical and rapidly progressive even on appropriate anti-Legionella antimicrobial therapy. Spontaneous unilateral pneumothorax is a rare radiographic manifestation of Legionnaires' disease. We present a case of a young male who is presenting clinical finding was that of spontaneous bilateral pneumothoraces due to Legionella CAP. We believe this is the first reported case of Legionnaires' disease presenting as spontaneous bilateral pneumothoraces. Clinicians should be aware of the protean radiological manifestations of Legionnaires' disease. In patients presenting with CAP and unilateral or bilateral spontaneous pneumothorax, clinicians should have Legionnaires' disease in the differential diagnosis.

Severe Legionella pneumonia: rapid presumptive clinical diagnosis with Winthrop-University Hospital's weighted point score system (modified)

Legionnaires' disease is a systemic infection involving the lungs and accompanied by a characteristic pattern of extrapulmonary organ involvement. Legionnaires' disease is one of the non-zoonotic causes of atypical community-acquired pneumonia (CAP). Legionnaires' disease commonly presents as severe CAP requiring hospitalization and intensive care. Each atypical CAP has its own characteristic pattern of extrapulmonary laboratory clinical findings and abnormalities that are the basis of clinical syndromic diagnosis. Studies have been unsuccessful in identifying individual clinical and laboratory parameters that are specific for Legionella. Individually, clinical and laboratory abnormalities lack diagnostic specificity. The diagnostic specificity of clinical and laboratory findings is increased when combined and are the basis of a clinical syndromic diagnosis. The importance of serial nonspecific laboratory abnormalities with Legionnaires' disease is emphasized. The sensitivity and specificity of a clinical syndromic diagnosis are enhanced if they are based on a weighted point score system. A diagnostic weighted point score system is based on the varying diagnostic importance of clinical and laboratory diagnostic findings. The Winthrop-University Hospital's Infectious Disease Division's rapid clinical diagnostic weighted point system is based on a weighted point score of clinical and laboratory findings. The case presented is that of a 55-year-old man with severe CAP who required hospitalization and intensive care admission. The presumptive clinical diagnosis of Legionella CAP was based on the Winthrop-University Hospital Infectious Disease Division's weighted point score system, which permitted early empiric anti-Legionella antimicrobial therapy and prompted specific Legionella testing. Legionnaires' disease is definitively diagnosed by serology or a urinary Legionella antigen test. This case of severe Legionnaires' CAP was confirmed by urinary antigen test reported on hospital day 6. The Winthrop-University Hospital is weighted point score system (modified) permits a rapid clinical presumptive diagnosis of Legionnaires' disease and is an accurate predictor of Legionella CAP.