01Approach to the Critical Patient/attcp42

Immediate stabilization priorities

›Airway and oxygenation threats

›Supplemental oxygen to maintain SpO2 >= 94%

›High-flow nasal cannula for moderate hypoxemia

›Early intubation for progressive respiratory failure

›Ventilation failure markers

›Rising PaCO2 on ABG

›Respiratory fatigue or use of accessory muscles

›If unable to protect airway, proceed to definitive airway management

›Rapid sequence intubation preparation

›Class I recommendation

›Circulation and sepsis threats

›Hemodynamic instability criteria

›SBP < 90 mmHg or MAP < 65 mmHg

›Lactate >= 2 mmol/l

›IV fluid resuscitation for dehydration from fever and diarrhea

›30 ml/kg crystalloid bolus in septic shock

›Reassess volume status after each bolus

›Vasopressors if septic shock persists

›Norepinephrine first-line

›ICU-level care required

Alarm features triggering escalation

›Rapidly progressive multilobar infiltrates despite antibiotics

›>50% of patients show radiographic progression in week 1 despite appropriate therapy

›Do not change antibiotics based on imaging alone

›Respiratory failure requiring mechanical ventilation

›ICU admission in nearly one-third of Legionella pneumonia cases

›ARDS protocol if bilateral infiltrates with refractory hypoxemia

02History/hx52

Exposure history

›Incubation period and source

›Incubation 2-14 days before symptom onset

›Hotel or resort stays within prior 2 weeks

›Cruise ships or hot tub or spa exposures

›Cooling towers, hospital water systems, decorative fountains

›Occupational exposure to plumbing, HVAC maintenance, or construction near water systems

›Cluster history

›Other individuals from same hotel, workplace, or building also ill

›Cluster identification essential for public health response

Symptom characterization

›Prodrome and systemic features

›Headache, myalgia, asthenia, anorexia preceding respiratory symptoms

›High fever often >40 degrees C

›Relative bradycardia (pulse-temperature dissociation) classically described

›Respiratory symptoms

›Cough in 41-92% of cases

›Initially dry, progressing to mildly productive

›Dyspnea in 36-56% of cases

›Pleuritic chest pain in 14-50% of cases

›Gastrointestinal symptoms (hallmark feature)

›Watery non-bloody diarrhea in 19-47%

›Nausea and vomiting in 9-25%

›Abdominal pain

›Prominent GI symptoms in a pneumonia patient is a classic clue

›Neurological symptoms

›Headache and confusion and obtundation present in 38-53%

›Seizures in severe cases

03Physical Exam/exam40

Vital signs

›Stability snapshot

›Temperature: High fever often >38.8 degrees C

›Hypothermia as severe sepsis marker in immunocompromised

›Respiratory rate >= 30 per minute as severity marker

›Rising trend as respiratory fatigue marker

›Blood pressure

›SBP < 90 mmHg

›MAP < 65 mmHg

›Heart rate

›Relative bradycardia despite high fever (pulse-temperature dissociation)

›Classically described though nonspecific

›Oxygen saturation on room air

Pulmonary exam

›Chest findings

›Crackles and bronchial breath sounds

›May be unilateral early, progressing to bilateral

›Signs of consolidation including egophony

›Reduced breath sounds at base if pleural effusion

›Dullness to percussion over effusion

›Present in 15-50% at admission

Neurological and abdominal exam

›Neurological assessment

›Confusion and obtundation

›New delirium as severity marker

›Focal neurological deficits

›Seizures in severe cases

›Abdominal findings

04Differential Diagnosis/ddx37

Life threats and close mimics

›Other atypical pneumonias

›Mycoplasma pneumoniae

›Younger patients and milder course

›More upper respiratory symptoms and less GI involvement

›ICD-10 J15.7

›Chlamydia psittaci

›Bird exposure history

›Similar atypical presentation but less severe cough

›Q fever (Coxiella burnetii)

›Animal exposure and hepatitis

›Atypical pneumonia pattern

›Streptococcus pneumoniae pneumonia

›Most common CAP organism

›Less likely to have prominent GI or neurological symptoms

›Responds to beta-lactams

›ICD-10 J13

›Influenza and COVID-19 pneumonia

›Viral prodrome and myalgias

›Confirm with NAAT

›ICD-10 J09-J11 and U07.1

Immunocompromised-specific differentials

›Pneumocystis jirovecii pneumonia (PJP)

›Bilateral ground-glass opacities

›Elevated LDH

›Severely immunocompromised host

›ICD-10 B59

›Tuberculosis

05Laboratory Tests/lt51

Legionella-specific diagnostic testing

›Urinary antigen test (UAT)

›First-line rapid test

›Result available in 15 minutes

›Remains positive for weeks after infection

›Sensitivity 56-99%; only detects L. pneumophila serogroup 1

›Serogroup 1 accounts for 80-90% of community-acquired cases

›Negative UAT does not exclude non-serogroup 1 or other Legionella species

›Legionella PCR (respiratory specimens)

›Superior sensitivity approximately 97%

›Detects all serogroups and Legionella species

›Sputum, BAL, or endotracheal aspirate preferred

›IDSA and ASM recommend PCR as preferred early diagnostic modality (2024 update)

›Respiratory culture on BCYE agar

›Gold standard for definitive diagnosis

›Slow (3-5 days) — not useful for acute management

›Required for environmental source matching in outbreaks

›Serology (antibody titers)

›Not useful acutely

›Seroconversion takes >= 3 weeks

›Seroconversion never occurs in approximately 25% of culture-proven cases

Characteristic laboratory abnormalities

›Electrolytes

›Hyponatremia (Na < 130 mmol/l)

›More frequent in Legionella than other pneumonias

›Multifactorial — SIADH and GI losses

›Hypophosphatemia

›Common finding; aetiology not fully elucidated

06Diagnostic Tests/dt65

Scoring Systems

›Pneumonia severity scoring for disposition

›PSI (Pneumonia Severity Index) — preferred over CURB-65 for Legionella

›Broader comorbidity integration

›Class IV-V warrants admission; class V warrants ICU consideration

›CURB-65

›Confusion

›Urea > 7 mmol/l

›Respiratory rate >= 30 per minute

›Blood pressure SBP < 90 mmHg or DBP <= 60 mmHg

›Age >= 65 years

›Score 0-1: outpatient candidate in most cases

›Score >= 2: admission; >= 3: higher mortality and ICU consideration

›qSOFA as bedside sepsis screening tool

›RR >= 22 per minute

›SBP <= 100 mmHg

›Altered mental status

›Positive qSOFA triggers full sepsis evaluation

›Limitations of scoring

›Legionella-specific risk not fully captured by generic pneumonia scores

›Immunocompromised patients may be underscored

›Clinical trajectory supersedes single score

›ACEP Level C recommendation for score use as adjunct only

MRI

›MRI chest role in Legionnaires disease

›Limited acute utility

›Availability constraints and motion artifact risk

›Unstable patients cannot safely undergo MRI

07Disposition/dispo40

ICU admission criteria

›ICU indications

›Mechanical ventilation requirement

›Intubation for respiratory failure

›HFNC with escalating oxygen requirement

›Septic shock

›Vasopressor requirement despite adequate fluid resuscitation

›Lactate > 2 mmol/l with organ dysfunction

›Multiorgan failure

›Rhabdomyolysis with acute renal failure

›CNS involvement with obtundation or seizures

›Nearly one-third of Legionella pneumonia cases require ICU care

Ward admission criteria

›Admission indications

›Hypoxemia

›SpO2 < 92% on room air

›Escalating supplemental oxygen requirement

›Hemodynamic concern without ICU-level instability

›SBP < 90 mmHg responding to fluids

›Lactate >= 2 mmol/l improving with resuscitation

›Inability to tolerate oral medications

›Persistent vomiting or diarrhea

›High fever with dehydration

›Severity score threshold

›CURB-65 >= 2 or PSI class IV-V

›Significant comorbidities with decompensation risk

›Immunocompromised host requiring IV antibiotics

08Treatment/t69

Initial stabilization

›Supportive measures

›Supplemental oxygen

›Nasal cannula titrated to SpO2 >= 94%

›HFNC for moderate-to-severe hypoxemia (FiO2 > 40% requirement)

›Early intubation for progressive respiratory failure or inability to protect airway

›IV fluid resuscitation

›Aggressive hydration especially with fever and diarrhea

›30 ml/kg crystalloid in septic shock

›Reassess after each bolus to avoid fluid overload

›Vasopressors if septic shock

›Norepinephrine 0.01-3 mcg/kg/min IV

›Titrate to MAP >= 65 mmHg

›Electrolyte correction

›Hyponatremia: cautious correction 6-8 mmol/l per 24 hours

›Hypophosphatemia: oral or IV replacement per severity

Antibiotic therapy — first-line agents

›Fluoroquinolones (preferred for severe disease)

›Levofloxacin IV or PO

›750 mg once daily

›IV until clinical improvement, then oral step-down

›Duration: 5-10 days standard; 14-21 days immunocompromised

›Moxifloxacin PO

›400 mg once daily

›QT prolongation risk — review baseline ECG

›Duration: 5-10 days

›Systematic review and meta-analysis (Jasper 2021): fluoroquinolones associated with shorter time to clinical stability versus macrolides

›Macrolides

›Azithromycin IV

›500 mg once daily IV until clinical improvement

›Step down to PO azithromycin 500 mg once daily

›Duration: 3-5 days standard; up to 10 days for severe or immunocompromised

›Azithromycin PO (outpatient mild disease)

›500 mg once daily

›3-5 day course for mild disease in immunocompetent

›Older macrolides (erythromycin, clarithromycin) — avoid in transplant patients

›CYP450 interactions with tacrolimus and cyclosporine

›Use fluoroquinolone, doxycycline, or azithromycin instead

Antibiotic therapy — alternatives

›Doxycycline

›Acceptable alternative when fluoroquinolone and macrolide not suitable

›100 mg PO or IV twice daily

›Duration: 10-14 days; extend to 21 days immunocompromised

›Avoid in pregnancy (Category D)

›Combination therapy

›No evidence supports macrolide plus fluoroquinolone combination over monotherapy

›Even for severe disease — ACEP Level B recommendation

›Monotherapy with appropriate agent is standard of care

›Parenteral to oral step-down

›Switch to oral when afebrile >= 24-48 hours and tolerating oral medications

›Equivalent bioavailability for fluoroquinolones and azithromycin

›Do not stop antibiotics until afebrile >= 48-72 hours

Duration of therapy

›Duration by agent and host

›Levofloxacin 5-10 days immunocompetent; 14-21 days immunocompromised

›Azithromycin 3-5 days mild-moderate; up to 10 days severe or immunocompromised

›Doxycycline and other agents 10-14 days; extended to 21 days immunocompromised

Rhabdomyolysis management

›Monitoring and treatment

›Serial CK measurements every 6-12 hours until peak identified and trending down

›Target urine output >= 200-300 ml/hr with aggressive hydration

›IV normal saline or lactated Ringer's to maintain urine flow

›Renal replacement therapy if oliguria or anuria despite resuscitation

›Nephrology consult for acute kidney injury

Respiratory failure management

›Ventilatory support pathway

›HFNC trial for PaO2/FiO2 < 200 mmHg

›Flow 40-60 L/min; FiO2 titrated to SpO2 >= 94%

›Reassess hourly — rapid deterioration common

›Lung-protective ventilation if intubated

›Tidal volume 6 ml/kg ideal body weight

›Plateau pressure < 30 cmH2O

›PEEP titrated to oxygenation response

›Prone positioning for severe ARDS (PaO2/FiO2 < 150 mmHg)

›>= 16 hours per session

09Special Populations/sp63

Pregnancy

›Maternal considerations

›Aspiration and pneumonia risk

›Increased immunosuppressed state of pregnancy

›Delayed gastric emptying increases aspiration risk

›Maternal hypoxemia directly compromises fetal oxygenation

›Fetal monitoring

›Continuous fetal monitoring when viable gestation

›Maternal SpO2 target >= 95% to protect fetal oxygenation

›Antibiotic selection in pregnancy

›Azithromycin: Category B — generally safe; first-line for atypical pneumonia in pregnancy

›500 mg once daily PO or IV

›Duration 5-7 days

›Levofloxacin: Category C — use when benefits outweigh risks for severe disease

›Theoretical concern for fetal cartilage; generally avoided in first trimester

›Consider for life-threatening Legionella in second or third trimester

›Doxycycline: Category D — avoid in pregnancy

›Fetal bone and tooth development impairment

›Erythromycin: avoid due to cholestatic hepatitis risk in pregnancy

›Imaging in pregnancy

›CXR with abdominal shielding when clinically indicated

›Radiation risk is low; do not withhold necessary imaging

›CT chest only when benefits outweigh radiation risks

›MRI preferred if CT not essential

Geriatric

›Atypical presentation

›Afebrile infection common in older adults

›Occult sepsis risk without fever

›Delirium as primary or only symptom

›Lower respiratory rate threshold for concern

›Age-related reduced respiratory reserve

›Pharmacological considerations

›Renal dosing adjustment required

›Levofloxacin dose reduction for CrCl < 50 ml/min

›CrCl >= 20 and < 50: 500 mg loading then 250 mg daily

›QT prolongation risk higher in older adults

›Baseline ECG before fluoroquinolone

›Review concurrent QT-prolonging medications

›Doxycycline: esophageal irritation risk — ensure adequate hydration and upright positioning

›Disposition bias

›Lower threshold for admission in frail or cognitively impaired patients

›Limited home support for IV antibiotic completion

›Swallow dysfunction prevalence increases falls and aspiration risk

›Functional status reassessment critical for discharge planning

Pediatrics

›Epidemiology in children

›Legionnaires disease less common in immunocompetent children

›Nosocomial cases in neonatal and pediatric ICU settings

›Immunocompromised children (transplant, oncology) at highest risk

›Antibiotic selection in children

›Azithromycin — first-line for children

›10 mg/kg once daily (maximum 500 mg) PO or IV

›Duration: 5-7 days immunocompetent; up to 10 days immunocompromised

›Levofloxacin — acceptable when azithromycin not suitable

›8-10 mg/kg IV or PO twice daily for children < 5 years (maximum 250 mg per dose)

›10 mg/kg once daily for children >= 5 years (maximum 500 mg)

›Use restricted to severe or fluoroquinolone-indicated cases

›Doxycycline — avoid in children < 8 years (dental staining)

›May be used in children >= 8 years: 2.2 mg/kg per dose twice daily (maximum 100 mg per dose)

›Clinical features in children

›Similar to adults but GI symptoms and neurological involvement may predominate

›Diarrhea and confusion in school-age children and adolescents

›Rhabdomyolysis less frequent than in adults

›Respiratory failure management

›Age-appropriate oxygen thresholds and tidal volume targets

›Feeding intolerance as severity marker in infants

10Background/b65

Epidemiology

›Incidence and burden

›Legionella accounts for approximately 5% of all-cause community-acquired pneumonia

›One of three most common causes of CAP requiring ICU admission

›Notifiable disease in most jurisdictions worldwide

›Mortality range 4-40% depending on host factors and treatment timing

›Higher mortality in immunocompromised and ICU patients

›Early appropriate antibiotic therapy significantly reduces mortality

›Approximately one-third of cases require ICU-level care

›Demographics

›Age > 50 years and male sex predominate

›Rare in immunocompetent children

›Seasonal peak: June-October (Northern Hemisphere)

›Relates to cooling tower use and warm-water system proliferation

›Sporadic and outbreak forms

›Sporadic cases: individual exposures to contaminated water

›Outbreak cases: shared water source (hotel, hospital, cooling tower)

›Causative organisms

›Legionella pneumophila serogroup 1: 80-90% of community-acquired cases

›Other serogroups and non-pneumophila species account for remaining cases

›Non-serogroup 1 strains missed by urinary antigen test

›Over 60 Legionella species identified; approximately 20 associated with human disease

Pathophysiology

›Mechanism of infection

›Inhalation of aerosolized water droplets containing Legionella

›Person-to-person transmission does not occur

›Water system contamination is required source

›Obligate intracellular pathogen

›Survives and replicates within alveolar macrophages

›Evades phagolysosomal killing — explains why beta-lactams are ineffective

›Intracellular location requires agents with intracellular penetration (macrolides, fluoroquinolones)

›Multiorgan involvement

›Pulmonary: alveolar macrophage invasion leading to pneumonia and ARDS

›Renal: direct invasion and rhabdomyolysis-related acute tubular necrosis

›Neurological: mechanisms include direct CNS invasion, hyponatremia, and inflammatory cytokines

›Cardiac: myocarditis and pericarditis via direct tissue invasion and systemic inflammatory response

›Hepatic: transaminase elevation from direct invasion and systemic inflammation

›Immune response

›Cell-mediated immunity is primary host defense

›T-cell activation required for macrophage bactericidal function

›Explains severity in T-cell-deficient states (transplant, hematologic malignancy, HIV)

›Humoral immunity less protective

›Antibody production delayed and incomplete

Therapeutic Considerations

›Antibiotic mechanism of action

›Fluoroquinolones: inhibit DNA gyrase and topoisomerase IV with excellent intracellular penetration

›Achieve high intracellular concentrations in alveolar macrophages

›Superior time to clinical stability in meta-analysis (Jasper 2021)

›Macrolides: inhibit bacterial protein synthesis; concentrate in macrophages and lung tissue

›Immunomodulatory effects may provide additional benefit

›Doxycycline: tetracycline class with intracellular activity

›Acceptable alternative when fluoroquinolone and macrolide not suitable

›Beta-lactams and aminoglycosides are ineffective

›Cannot penetrate intracellular compartment where Legionella resides

›Radiographic progression paradox

›>50% of patients show imaging progression in first week despite appropriate antibiotics

›Expected phenomenon — do not change or add antibiotics based on imaging alone

›Clinical improvement (fever, respiratory status) is the primary treatment response measure

›Radiographic clearance lags behind clinical improvement by weeks

›Combination therapy evidence

›No evidence supports combination macrolide plus fluoroquinolone over monotherapy

›Even in severe disease — Cunha et al. 2016

›ACEP Level B recommendation for monotherapy with appropriate intracellular agent

›Prevention

›Water system maintenance and decontamination is primary prevention

›Superheating (>60 degrees C) and chlorination of building water systems

›Cooling tower maintenance with biocides

›No vaccine available for Legionella

11Patient Discharge Instructions/pdi31

copy discharge instructions

›Legionnaires disease home care instructions

›Take antibiotics exactly as prescribed until the full course is completed

›Do not stop antibiotics early even if feeling better

›Complete the full prescribed duration

›Rest and stay well hydrated

›Drink at least 8 glasses of water or clear fluids daily

›Avoid alcohol during antibiotic course

›Manage fever

›Acetaminophen or ibuprofen as directed for fever and muscle aches

›Fever may persist for several days after starting antibiotics

›Warning signs — return to emergency department immediately

›Worsening shortness of breath at rest

›New oxygen requirement or home oxygen saturation below 92%

›Chest pain

›Blue or grey lips or fingernails

›Confusion, difficulty thinking clearly, or loss of consciousness

›Recurrent high fever after initial improvement

›Dark or bloody urine or significantly decreased urine output

›Persistent vomiting or inability to keep down oral medications or fluids

›Expected recovery course

›Clinical improvement typically within 3-5 days of appropriate antibiotics

›Fatigue, weakness, and cognitive symptoms may persist for weeks to months after recovery

›Radiographic resolution on chest X-ray may lag behind clinical recovery by weeks

›No transmission to household contacts

›Legionella is not spread person-to-person

›Household contacts do not require antibiotics or testing

›Follow-up plan

12References/r20

Guidelines and key sources

›Primary clinical guidelines

›IDSA and ATS: Diagnosis and Treatment of Adults With Community-Acquired Pneumonia — Metlay JP et al., American Journal of Respiratory and Critical Care Medicine, 2019

›IDSA and ASM: Guide to Utilization of the Microbiology Laboratory for Diagnosis of Infectious Diseases, 2024 Update — Miller JM et al., Clinical Infectious Diseases, 2024

›File TM, Ramirez JA: Community-Acquired Pneumonia — New England Journal of Medicine, 2023

›Key Legionella references

›Rello J, Allam C, Ruiz-Spinelli A, Jarraud S: Severe Legionnaires Disease — Annals of Intensive Care, 2024

›Cunha BA, Burillo A, Bouza E: Legionnaires Disease — Lancet, 2016

›Phin N, Parry-Ford F, Harrison T et al: Epidemiology and Clinical Management of Legionnaires Disease — Lancet Infectious Diseases, 2014

›Diagnostic and treatment evidence

›Jasper AS, Musuuza JS, Tischendorf JS et al: Fluoroquinolones versus macrolides for Legionella pneumonia — Clinical Infectious Diseases, 2021

›Avni T, Bieber A, Green H et al: Diagnostic Accuracy of PCR versus urinary antigen for Legionella — Journal of Clinical Microbiology, 2016

›Sopena N, Sabria-Leal M, Pedro-Botet ML et al: Comparative Clinical Presentation of Legionella versus other CAP — Chest, 1998

›Imaging and outcomes

›Kim KW, Goo JM, Lee HJ et al: CT findings and clinical features of Legionella pneumonia — Journal of Computer Assisted Tomography, 2007

›Shroff GS, Marom EM, Wu CC et al: Pulmonary Legionellosis in oncologic patients on CT — Journal of Computer Assisted Tomography, 2016

›Allgaier J, Lagu T, Haessler S et al: Risk factors, management and outcomes of Legionella pneumonia — Chest, 2021

›ICD-10 coding

›ICD-10 A48.1 Legionnaires disease

›ICD-10 A48.2 Nonpneumonic Legionnaires disease (Pontiac fever)

›SNOMED CT Legionella pneumophila pneumonia concept

Evidence & Review

Evidence & Review