TABLE 4.
C. difficile hamster challenge model using five of the most prevalent representative toxin variant strains
| Challenge prototype strain, toxin production profile (spore inoculum used for challenge) | Resulta |
Between-group statistical analysesb | |||
|---|---|---|---|---|---|
| Placebo |
C. difficile toxoid vaccine |
||||
| Observations (symptoms) | Lethality rate | Observations (symptoms) | Lethality rate | ||
| Toxinotype 0 strain 630 (RT 012), A+B+CDT− (3,700 CFU) | Onset of diarrhea (score 1) after 3 days with severe diarrhea (score 3) within 8 days after challenge | 8/9 (89) by 13 days | Very limited change in feces (score 1, loose stool) | 0/9 (0) | Symptoms, P < 0.0001 (Wilcoxon two-sample test); lethality, P = 0.0004 (Fisher exact test), P = 0.0001 (Kaplan-Meier log rank test) |
| Toxinotype III strain IPP40348 (RT 027), A+B+CDT+ (5,000 CFU) | Onset of diarrhea (score 1) after 2 days with severe diarrhea (score 3) within 3 days after challenge | 12/12 (100) by 4 days | 2 with moderate diarrhea (score 2; wet tail and perianal region) within 3 days that died 6 days after challenge | 2/12 (17) by 2 days | Symptoms, P < 0.0001 (Wilcoxon two-sample test); lethality, P < 0.001 (Fisher exact test), P ≤ 0.025 (Kaplan-Meier log rank test) |
| Toxinotype IV strain NK91 (RT 023), A+B+CDT+ (1,200 CFU) | Onset of diarrhea (score 1) within 1 day with severe and acute diarrhea (score 3) within 3 days after challenge | 12/12 (100) by 6 days | Mild and transient diarrhea (score 1) which resolved within 13 days | 0/12 (0) | Symptoms, P < 0.0001 (Wilcoxon two-sample test); lethality, P < 0.001 (Fisher exact test), P < 0.001 (Kaplan-Meier log rank test) |
| Toxinotype V strain BAA-1875 (RT 078), A+B+CDT+ (6,380 CFU) | Severe acute diarrhea (score 3) in 50% of hamsters within 2 days with rapid lethality onset | 12/12 (100) by 3 days | No disease symptoms | 0/12 (0) | Symptoms, P < 0.0001 (Wilcoxon two-sample test); lethality, P ≤ 0.0001 (Fisher exact test), P ≤ 0.0001 (Kaplan-Meier log rank test) |
| Toxinotype VIII strain ATCC 43598 (RT 017), A−B+CDT− (9,400 CFU) | Severe diarrhea (score 3) within 3 to 13 days after challenge | 7/12 (58) within 10 days | No disease symptoms | 0/12 (0) | Symptoms, P < 0.0001 (Wilcoxon two-sample test); lethality, P = 0.0046 (Fisher exact test), P = 0.0020 (Kaplan-Meier log rank test) |
For observations (symptom) data, diarrheal disease was reported as a group median score representing individual illness scores defined as follows: 0, no disease; 1, loose feces; 2, wet tail and perianal region; 3, wet perianal region, belly, and hind paws; 4, death. For lethality rate data, values represent the number of hamsters that died/total number of hamsters assessed (percent total deaths).
The area under the curve of the diarrheal disease scores over time was calculated for each animal. The effect on diarrheal disease symptoms (vaccine versus placebo) was analyzed using an exact Wilcoxon two-sample test. Protection efficacy was assessed as the difference between the survival kinetic percentages (Kaplan-Meier log rank test) and as the difference between the survival percentages 17 days after challenge (Fisher exact test). Both statistical tests were performed with a margin of error of 5%.