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Volume 32, Number 9—September 2026
Research
Clustering and Source Association of Clinical and Nonclinical Listeria monocytogenes Isolates, New York, USA, 2000–20211
Table 5
Characteristics of food-clinical Listeria monocytogenes isolate pairs used in the analysis of time between food isolate collection and subsequent detection of a genetically related clinical isolate by SNP cluster in study of clustering and source association of clinical and nonclinical L. monocytogenes isolates, New York, USA, 2000–2021*
| CC | SNP cluster | Food category | No. food–clinical isolate pairs† | No. distinct food isolates | No. distinct clinical isolates linked with food isolates by<50 SNPs | inlA PMSC types in food and clinical isolates‡ |
|---|---|---|---|---|---|---|
| CC1 | PDS000003335§ | Processed dairy | 1 | 1 | 1 | None |
| PDS000025547 | Processed meat | 3 | 1 | 3 | None | |
| PDS000082531 | Processed dairy | 1 | 1 | 1 | None | |
| PDS000091530 |
Raw dairy |
1 |
1 |
1 |
None |
|
| CC5 | PDS000024625 | Processed dairy | 1 | 1 | 1 | None |
| PDS000024647 |
Salad |
7 |
1 |
7 |
None |
|
| CC6 | PDS000025014 | Processed dairy | 5 | 1 | 5 | None |
| PDS000025078§ |
Processed meat |
23 |
1 |
23 |
None |
|
| CC7 |
PDS000003277 |
Processed meat |
3 |
1 |
3 |
None |
| CC8 | PDS000025311 | Raw dairy | 2 | 1 | 2 | None |
| Processed fish |
1 |
1 |
1 |
None |
||
| CC88 |
PDS000003204 |
Processed fish |
3 |
1 |
3 |
None |
| CC121 |
PDS000024645 |
Processed fish |
2 |
2 |
1 |
Type 6 |
| CC155 | PDS000024385 | Salad¶ | 1 | 1 | 1 | None |
| PDS000024989§ |
Raw meat¶ |
13 |
1 |
13 |
None |
|
| CC199 | PDS000083553# | Processed fish | 2 | 2 | 1 | Type 4 |
| Processed meat |
1 |
1 |
1 |
Type 4 |
||
| CC204 |
PDS000003073 |
Salad¶ |
2 |
1 |
2 |
None |
| CC226 |
PDS000025453 |
Raw dairy |
1 |
1 |
1 |
None |
| CC321 | PDS000000366§ | Processed fish | 7 | 5 | 3 | Type 3 |
| Processed meat¶ |
96 |
9 |
12 |
Type 3 |
||
| CC369 |
PDS000090530 |
Produce |
1 |
1 |
1 |
None |
| CC388 |
PDS000043055 |
Raw dairy |
1 |
1 |
1 |
None |
| CC389 |
PDS000024852 |
Raw dairy |
1 |
1 |
1 |
None |
| CC554 | PDS000003170 | Processed fish | 8 | 1 | 8 | None |
| PDS000003173 |
Raw dairy |
6 |
1 |
6 |
None |
|
| CC573 | PDS000000308 | Produce | 12 | 3 | 5 | None |
*CC, clonal complex; PMSC, premature stop codon; SNP, single-nucleotide polymorphism. †Not all food–clinical isolate pairs met the <50 SNP threshold and, therefore, the number of food–clinical isolate pairs is not necessarily equal the number of food isolates times the number of clinical isolates in each SNP cluster. ‡When detected, inlA PMSC was present in all food and clinical isolates used in this analysis within the corresponding SNP cluster. When inlA PMSC was not detected, it was indicated as none. §Indicates SNP clusters that had formal outbreak investigations. In our analysis, PDS000003335 had 1 clinical isolate that was linked with 1 processed dairy isolate (by 2 SNPs); PDS000025078 had 9 clinical isolates that were linked with 1 processed meat isolate (3–9 SNPs); PDS000024989 had 2 clinical isolates that were linked with 1 raw meat isolate (0–2 SNPs), and PDS000000366 had 4r clinical isolates that were linked with 9 processed meat isolates (2–50 SNPs). Among those, 2 outbreak investigations (for the isolates in PDS000025078 and PDS000000366) had processed meat as the implicated food source, whereas the remaining investigations did not have a confirmed source. ¶These SNP clusters had other food categories matching to the clinical isolates by <50 SNPs. For clinical isolates associated with multiple food categories, only the clinical–food isolate pairs with the lowest pairwise SNP distance were retained. #For this SNP cluster, 2 food isolates from different food categories had the same minimum SNP distance to the same clinical isolate, and both food-clinical isolate pairs were retained.
1Preliminary results from this study were presented at the 2025 International Association for Food Protection Conference; July 27–30, 2025; Cleveland, Ohio, USA.