CDC and ISO 11731 Legionella Methods Comparison
| CDC Method | ISO 11731 Meth | |
| Sample Hold Time/Shipping | No hold time. Samples should be refrigerated if not processed within 72 hours from collection. | 48 hour hold time. Samples should be received by the lab within 24 hours of collection to be processed within 48 hours after sample collection. |
| Sample Shipping Temperature | Samples should be refrigerated. Samples should be shipped in insulated coolers to protect against extreme heat or cold. | Ambient temp shipping is allowed. Samples should be shipped in insulated coolers to protect against extreme heat or cold. |
| Sample Temperature in the Lab | If samples cannot be processed within 72 hours they should be refrigerated. | If not processed immediately upon receipt, samples should be refrigerated at 6°C +/- 2°C |
| Pre-Treatment | Non-potable samples are direct plated with and w/o acid-treatment. Potable samples are filter concentrated with acid-treatment only if overgrowth of plated sample occurs. | All samples (potable and non- potable) are filter concentrated. Aliquots are left untreated, acid treated and heat treated prior to plating. |
| Legionella Confirmation | Growth on BCYE agar containing iron and L- Cysteine incubated for 24 hours. | Growth on BCYE agar containing iron and L-Cysteine incubated for 48 hours. |
| Legionella Identification | Latex Agglutination or Direct Fluorescent Antibody (DFA) | Direct Fluorescent Antibody (DFA) |
| Incubation Time | Examine plates on days 4 and 7. If new Legionella growth is seen on day 7, then incubate for 10 days. | Examine plates on days 4, 7 and 10. Positive results may be reported on day 7 but plates must be incubated for 10 days to confirm a negative result. |
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