Listeriosis Outbreaks in British Columbia, Canada, Caused by Soft Ripened Cheese Contaminated from Environmental Sources
Table 2
Results of lab tests in milk, cheese, and environmental samples.
Outbreak A
Outbreak B
Milk samples
Raw milk SPC (log10 CFU/mL)
(1) Government dairy pool
3.90
n/a
(2) Local farm—cow
n/a
3.00
(3) Local farm—goat
4.43
n/a
Raw cow milk L.m.
Absent
Absent
Raw cow milk pH
NT
6.8
Pasteurized cow milk phosphatase
Negative
Negative
Cheese samples
Number of cheese samples L.m. + (tested)
16 (25)
22 (29)
Number of varieties + (number of lots+)
8 (12)
3 (3)
L.m. counts (median log10 CFU/g)
2.0
2.0
L.m. counts (range log10 CFU/g)
<2 to 9.4
<2 to 9.0
Environmental samples
In the plant—ingredients
Number of L. spp. + (tested)
2 (33)
2 (32)
In the plant—surfaces
FCS number of L spp. + (tested)
3 (17)
0 (5)
NFCS number of L spp. + (tested)
2 (23)
0 (17)
Outside the plant
Number of L spp. + (tested)
1 (1)
4 (7)
On the hobby or dairy farm
Number of L spp. + (tested)
12 (14)
6 (14)
Number of environmental L.m. + (tested)
17 (88)
14 (75)
SPC, standard plate count; NT, not tested; n/a, not applicable; L.m., Listeria monocytogenes; L. spp., Listeria species (L. innocua, L. ivanovii or L. seeligeri); FCS, food contact surface; NFCS, nonfood contact surface.
