Table 1.
False-positive detection of infectivity with inactivated Cryptosporidium parvum oocysts
| Inactivation method | No. of oocysts inoculated | Wna | Cell culture wells positiveb (%) by: |
||
|---|---|---|---|---|---|
| IFA | PCR | RT-PCR | |||
| 70°C, 30 min | 10 | 20 | 0 | 0 | 0 |
| 100 | 20 | 0 | 0 | 0 | |
| 3×(LiqN2, 2 min/ 95°C, 1 min)c | 10 | 20 | 0 | 0 | 0 |
| 100 | 20 | 10 | 5 | 0 | |
| UV irradiation, ∼60 mJ/cm2 | 10 | 20 | 0 | 25 | 0 |
| 100 | 20 | 0 | 60 | 0 | |
| 0.5 kGy gamma irradiation | 100 | 20 | 0 | 55 | 0 |
| 100 | 15 | 0 | 45 | 0 | |
| 100 | 20 | 0 | 10 | 0 | |
| None (mock infectionsd) | 100 | 20 | 0 | 5 | 15 |
| 100 | 20 | 0 | 10 | 13e | |
| 25 | 10 | 0 | 0 | 0 | |
| 25 | 10 | 0 | 10 | 0 | |
| 25 | 10 | 0 | 0 | 20 | |
| None (unseeded wells) | 0 | 20 | 0 | 0 | 0 |
| None (untreated viable oocysts) | 10 | 40 | 62 | 65 | 45 |
a
Number of cell culture wells inoculated with each dose of oocysts.
b
Average of replicate experiments performed in two laboratories.
c
Three cycles of freezing in liquid nitrogen for 2 min followed by thawing at 95°C for 1 min.
d
Mock infections involved inoculating oocysts onto cell monolayers and then immediately processing the monolayers according to each of the detection assays.
e
Wn = 15.