Table 2.
Summary of diagnostic microbiological test parameters used to identify cases of injectional anthrax
| Case | HPS classification | PCR | Anti-PA IgG antibodies | Anti-LF IgG antibodies | Immunoreactive PA | Immunoreactive LF |
|---|---|---|---|---|---|---|
| A | Confirmed | Negative | Positive | Negative | Negative | Negative |
| B | Confirmed | Negative | Positive | Positive | Negative | Negative |
| C | Confirmed | Pus PCR positive | Negative | Negative | Not tested | Not tested |
| D | Confirmed | Blood and pus PCR positive | Positive | Positive | Negative | Negative |
| E | Confirmed | Tissue PCR positive | Positive | Positive | Negative | Negative |
| F | Confirmed | Pus PCR positive | Positive | Positive | Negative | Negative |
| G | Confirmed | Swab PCR positive for cap and lef genes | Positive | Positive | Negative | Negative |
| H | Probable | Negative | Positive | Negative | Negative | Negative |
| I | Probable | Negative | Positive | Negative | Negative | Negative |
| J | Probable | Negative | Equivocal | Negative | Positive | Equivocal |
| K | Probable | Negative | Positive | Equivocal | Negative | Negative |
| L | Probable | Negative | Positive | Negative | Not tested | Not tested |
| M | Possible | Negative | Equivocal | Negative | Negative | Negative |
| N | Possible | Negative | Negative | Positive | Negative | Negative |
| O | Possible | Negative | Positive | Negative | Negative | Negative |
| P | Possible | Negative | Equivocal | Equivocal | Negative | Negative |
| Q | Possible | Negative | Positive | Positive | Negative | Negative |
| R | Possible | Negative | Equivocal | Equivocal | Negative | Negative |
| S | Possible | Negative | Negative | Positive | Not tested | Not tested |
| T | Possible | Not tested | Positive | Positive | Not tested | Not tested |
| U | Possible | Negative | Positive | Negative | Not tested | Not tested |
HPS, Health Protection Scotland; PA, Protective antigen; LF, lethal factor.
In case G, although the full three genes required for PCR diagnosis were not present on the swab obtained, anthrax was confirmed from debrided tissue when the patient had surgery in another health board. In case C serology was tested on blood taken on day 8 after admission which might account for the negative serology despite the case being confirmed by PCR if seroconversion had not yet taken place. Cases A and B were classed as confirmed on the basis of rising titres of anti-PA IgG several days apart. For case A, the negative PCR result relates to peripheral blood PCR as no tissue or pus was received for PCR. For case B a single wound swab was received and was negative by PCR but as the patient had multiple sites of soft tissue infection at the time it is possible that a lesion was swabbed that did not have B. anthracis detectable whereas if sampling had been performed for all the lesions a different one may have tested positive by PCR.