| Method | Sensitivity | Specificity | Time to Result | Detects | Advantages | Limitations |
|---|---:|---:|---|---|---|---|
| Urinary antigen test (UAT) | 70-90% | ~100% | 15-30 min | *L. pneumophila* serogroup 1 antigen in urine | Rapid, widely available, useful first-line test, supports early targeted therapy (pqac-00000018) | Misses non-serogroup 1 *L. pneumophila* and other *Legionella* species; underestimates true epidemiology (pqac-00000018, pqac-00000022) |
| PCR / nucleic acid amplification test (respiratory specimen) | 96.8-97.7% | High | Hours to <24 h | All *Legionella* species/serogroups, depending on assay design | Higher sensitivity than UAT; detects non-Lp1 infections; rapid; useful on sputum/BAL (pqac-00000018, pqac-00000024) | Requires respiratory specimen and molecular lab capacity; assay standardization varies; some methods may detect nonviable organisms (pqac-00000018, pqac-00000020) |
| Culture (BCYE and related methods) | 50-80% | 100% | Days to weeks | All culturable *Legionella* species from respiratory/environmental samples | Gold standard; enables species/serogroup identification, typing, and outbreak source matching (pqac-00000017, pqac-00000020) | Slow; lower sensitivity than PCR; requires specialized media and expertise; affected by prior antibiotics (pqac-00000017) |
| Serology | Variable | Variable | Weeks | Host antibody response to *Legionella* | May support retrospective diagnosis or epidemiologic studies (pqac-00000017, pqac-00000024) | Not useful for early acute management; delayed seroconversion; immunosuppressed patients may not mount detectable antibodies (pqac-00000017) |
| Next-generation sequencing (NGS) / metagenomic sequencing | High analytical sensitivity; exact clinical sensitivity not yet standardized | High when sufficient sequence depth/interpretation is achieved | Typically 1-3 days, varies by platform | Broad pathogen detection, including fastidious/unexpected *Legionella* spp. | Unbiased detection; can identify multiple pathogens simultaneously; useful when routine tests are negative (pqac-00000017, pqac-00000023) | Expensive; limited availability; turnaround and bioinformatics burden; interpretation/contamination issues; not standard first-line testing (pqac-00000023) |
| Legiolert / Most Probable Number (MPN) | Not directly comparable to clinical sensitivity | Not directly comparable | ~7 days (environmental monitoring) | Environmental *L. pneumophila* in water systems | Practical for water-system surveillance and risk management; useful for prevention programs (pqac-00000020, pqac-00000030) | Environmental, not patient diagnosis; does not establish clinical disease by itself (pqac-00000020, pqac-00000030) |


*Table: This table summarizes the major diagnostic methods for Legionnaires' disease, including performance characteristics, turnaround times, and practical strengths and limitations. It is useful for comparing rapid clinical tests with confirmatory and environmental methods.*