Legionella in the City
An active NYC cluster raises the pretest probability in patients with pneumonia and a relevant 14-day exposure history. Test correctly. Cover atypicals early.
Current NYC cluster update ↗Ask about the Upper East Side
The active cluster centers on Carnegie Hill and Yorkville: ZIP codes 10028, 10128 and 10075.
Ask whether the patient lived, worked or visited there since late June. A Bronx address does not exclude exposure.
Positive cooling-tower PCR can detect live or dead bacteria. It does not confirm the outbreak source.
Risk rises with the host
- Age 50 or older
- Current or former smoking
- Chronic lung disease
- Cancer or immunocompromise
- Recent hospitalization, healthcare stay or travel
Collect exposure history for the 14 days before symptom onset.
Pneumonia plus systemic clues
No single symptom, laboratory abnormality or radiographic pattern is diagnostic. Outpatient beta-lactam failure is another clue.
Urine alone is incomplete.
Order the Legionella urinary antigen and a lower respiratory specimen for culture or molecular testing. The urine antigen usually detects only L. pneumophila serogroup 1. Sputum testing detects more types and can link a clinical isolate to an environmental source.
Collect both early. Do not delay antibiotics for specimen collection.
Who should get tested
- Pneumonia plus a current outbreak exposure
- Severe CAP or ICU-level illness
- Immunocompromised host
- Outpatient CAP treatment failure
- Recent healthcare stay or overnight travel
A negative urine antigen does not exclude non-serogroup 1 or non-pneumophila disease.
Cover intracellular disease
Ceftriaxone 1–2 g IV + azithromycin 500 mg IV/PO
or levofloxacin 750 mg IV/PO
- Use with the appropriate CAP regimen and local pathway
- Do not use beta-lactam monotherapy when Legionella is suspected
- Check QT risk, interactions and renal dosing
- Continue until clinically stable and for at least 5 days; extend for severe or complicated disease
Low threshold to admit
- Hypoxemia or escalating oxygen need
- Sepsis, hypotension or rising lactate
- Confusion, AKI or major electrolyte derangement
- Multilobar disease or rapid progression
- Immunocompromise or unreliable follow-up
What a tower result means
- Legionella spreads through inhaled contaminated water mist
- It is generally not spread person to person
- Current UES guidance says tap water and ordinary air conditioning remain safe
- A positive building test does not prove where a patient was infected
Report and preserve the isolate
- Document all locations visited during the prior 14 days
- Notify infection prevention for healthcare-associated exposure
- Report suspected or confirmed disease per NYC requirements
- Ensure respiratory culture is retained for public-health comparison