KA-2024-BHM-000008 - [2025] EWHC 2093 (KB)

Discussion

I have carefully considered all of the grounds and submissions that have been advanced on behalf of the Appellant by Mr Pennock. In my judgment, there were ample grounds for the judge’s conclusion that the Appellant’s illness was not caused by the cyclospora pathogen. There was evidence to support the findings made and the conclusions reached by the judge. The judge did not misunderstand the evidence, and the conclusions on the facts and the expert evidence were ones that a reasonable judge could reach. Furthermore, the judge gave more than adequate reasons for this conclusion.

There was no dispute that the regional laboratory recorded that cyclospora oocytes had been found in the Appellant’s stool sample, and the national reference laboratory did not find any cyclospora oocytes in the sample.

There was a dispute in the expert evidence about the conclusions to be drawn from the analyses of the Appellant’s stool samples that were carried out by the regional and the national reference laboratories, and the other evidence. Standing back, and looking at the matter in the round, it came down to which of the microbiology witnesses’ evidence the judge preferred.

The judge was plainly right to focus on the expert evidence of the microbiologists. The gastroenterologist who was instructed on behalf of the Appellant, Dr Bowling, accepted that he had to defer to the expert microbiologists on causation. Causation, for this purpose, included both the identification of the particular pathogen that had caused the illness, and then working out the source of the pathogen. The judge was fully entitled, and, indeed, undoubtedly right, to conclude from this that Dr Bowling could not help on the cyclospora or conclusion issues. The gastroenterologist who was instructed on behalf of the Respondent, Professor Bjarnason, also deferred to the microbiologists on issues of causation. To the extent that he strayed beyond the limits of his specialist expertise, and again quite rightly, the judge discounted his evidence.

This meant that the judge was faced with conflicting evidence from the microbiologists on the cyclospora issue. The Appellant’s expert, Professor Threlfall, held the view that, in light of the result of the tests at the regional laboratory, and notwithstanding the outcome of the tests at the national reference laboratory, it was clear that the Appellant had ingested cyclospora. Conversely, the Respondent’s expert, Dr Gant, held the opposite view: he considered that the court should rely upon the result of the test at the national reference laboratory, even though it contradicted the result at the regional laboratory. Both of the microbiology experts gave reasons for the view in reports, Part 35 Answers, and a joint statement, and their views were tested by cross-examination. The judge decided that he preferred Dr Gant’s view. He gave reasons for this decision, each of which was supported by the evidence:

Dr Gant had greater experience in testing for cyclospora oocytes. This was not in dispute. Professor Threlfall had accepted this. Dr Gant was Director at the National Hospital for Tropical Diseases. The national reference laboratory was based there and Dr Gant had ultimate responsibility for it;

The national reference laboratory had greater experience than the regional laboratories. This was borne out by the evidence. Cyclospora is not endemic or common in the UK and so regional laboratories are not used to testing for it. The national laboratory, on the other hand, is a national reference laboratory for a reason, because those who work there have the greatest experience in testing for what in UK terms are esoteric pathogens. This is why the purpose of the national reference laboratory was to check the initial findings of the regional laboratory. Dr Gant had said that laboratory technicians in the UK generally are not highly experienced whereas staff at the national reference laboratory have specific experience and training in identifying the organism. Professor Threlfall had accepted in evidence that the national reference laboratory testing was the” gold standard”. He also accepted that testing for cyclospora was “notoriously difficult”;

Dr Gant’s evidence on the testing process was more cogent that Professor Threlfall’s. Again, this was a conclusion that the judge could come to on the evidence. The judge accepted, as he was entitled to, Dr Gant’s evidence that there was no antibody for the oocyte, over Professor Threlfall’s evidence that there was such an antibody;

Professor Threlfall’s suggested explanation for why the oocytes had been found in the regional laboratory test, but not, a week or so later, in the national reference laboratory test, was therefore rejected. Professor Threlfall had said that the antibody deteriorated or degraded rapidly over time and so might have disappeared in the week or so between the first test and the second. Dr Gant said that they did not. Dr Gant said that “oocytes will remain detectable in a stool sample for extended periods of time, far exceeding the time elapsed in confirmatory testing by the reference laboratory.” When he was pressed on this issue in cross-examination, Professor Threlfall admitted that he could not point to any scientific papers to back up his assertion; and

In light of the above, on the balance of probabilities the positive result at the regional laboratory was a false positive.

The fact that there were points that could be made in favour of the conclusion that the Appellant had ingested cyclospora does not mean that the judge reached a conclusion that no reasonable judge could come to. It is almost always the case in a trial that there will be evidence pointing either way.

I now come to the specific grounds of challenge that are relied upon by Mr Pennock in relation to the cyclospora issue.

It is convenient to deal first with the contention that answers given by Dr Gant at the end of his cross-examination “destroyed” the Respondent’s case because the Respondent’s expert witness had accepted that the judge should proceed on the basis that it was probable that the Appellant had ingested cyclospora. In other words, Mr Pennock submitted that no reasonable judge could have done anything other than find in favour of the Appellant on the cyclospora issue, in light of the concession that was made by Dr Gant at the end of his cross-examination.

I am unable to accept this submission. The judge expressly referred to the evidence in question in his judgment. The judge found that Dr Gant had clarified what he had said in the relevant part of his cross-examination during his re-examination. The judge concluded that Dr Gant had made clear that he did not think that there was a probable finding of cyclospora oocytes.

In my judgment, the judge was entitled to come to this view and, indeed, he was plainly right to do so. The starting point is that, in his report and in the joint statement, Dr Gant had made absolutely clear that it was his view that the result obtained by the national reference laboratory was the one that should be relied on, and so that, when both results were taken together, the conclusion should be that there was no evidence of cyclospora oocytes in the Appellant’s stool sample. The passage in the cross-examination, upon which Mr Pennock places so much reliance, was a passage in which Mr Pennock was seeking to get the witness to accept that precedence should be given to the outcome of the test at the regional laboratory. Mr Pennock pointed out that Public Health England (PHE) and national and regional laboratories treat a positive test by a regional laboratory which is not subsequently tested by the national reference laboratory or another laboratory as a probable case of cyclospora. He asked Dr Gant whether there was any reason why the court should not take the same approach – i.e. that a single positive test is enough to prove cyclospora, even if there is no further confirmatory test. Dr Gant said that there were several reasons why the court should not take the same approach and treat it as a probable case of cyclospora. He explained that there were practical and pragmatic reasons why PHE treats a single positive test as a positive case of cyclospora. He explained that it was not a sensible use of resources to have a confirmatory test, especially as the test is expensive, and that it was necessary to move swiftly to treat the patient. The treatment, with co-trimoxazole, would be suitable for infections with similar pathogens and would not harm the patient even if, in fact, they do not have cyclospora.

So far, none of these answers amounted to a concession or in any way undermined the evidence that Dr Gant had given in support of the conclusion that the Appellant had ingested something other than cylosopora.

It was at this point in the cross-examination that Dr Gant concluded his answer with the words:

“So it’s epidemiological, it’s to do with pragmatism, limited resources, and it allows for definition to be put in place, and it’s probable and you’re right that’s how it is. So for the court that is what the particular specimen or this particular case might be described as.”

Mr Pennock considered that this answer gave him what he wanted and was a concession that the judge should treat the regional laboratory test as meaning that it was probable that the Appellant had tested positive for cyclospora. It was for that reason that he stopped his cross-examination at that point. Unfortunately, in my judgment, this answer, read in context, does nothing of the sort. It was simply saying that the court should understand that, for the purposes of the treatment of patients, and in accordance with PHE guidance, a single positive test for cyclospora at a regional laboratory is treated as a probable case of cyclospora. It was not a concession, contrary to all of Dr Gant’s evidence that had gone before, that the judge should treat the positive test at the regional laboratory as meaning on the balance of probabilities that the Appellant had ingested cyclospora, despite the result at the national reference laboratory.

That this is the right interpretation of Dr Gant’s evidence in cross-examination is confirmed by what he said immediately afterwards in re-examination. He was asked, “Given the two results, one by the local lab, one by the national reference lab, do you think on the balance of probabilities that is evidence of cyclospora?”. Dr Gant said, “No. In this specific case I do not. I agree that the paper work says probable. I do not believe in this case that cyclospora was ever involved.” In other words, Dr Gant was saying that, notwithstanding that the Health Service treated this as a probable case of cyclospora, the negative test at the national reference laboratory proved that it was not. Later in his re-examination, Dr Gant said, “I do not believe that cyclospora was found either.”

Accordingly, the answers given by Dr Gant in cross-examination did not mean that the judge was bound to find in the Appellant’s favour on the cyclospora issue.

The next question is whether, as Mr Pennock submitted, no reasonable judge could have found for the Respondent on the cyclospora issue, because the expert evidence of Dr Gant was fatally undermined by the fact that the particular reason why, in this case, Dr Gant took the view that the Appellant did not have cyclospora notwithstanding the positive result at the regional laboratory was because he had understood that she was ill before she left for Mexico. The judge found that the Appellant was not, in fact, ill before she left on holiday.

I do not accept this submission. It is clear from Dr Gant’s report, the joint statement, and his oral evidence that the fundamental reason why he concluded that the Appellant did not have cyclospora was because the outcome of the test conducted at the national reference laboratory was extremely reliable, and was to be preferred to the outcome of the test conducted by less experienced technicians at the regional laboratory. Put bluntly, his view, based on expertise and experience, was that the national reference laboratory was better at this sort of thing than the regional laboratory. Dr Gant said that the regional laboratories were not experienced in testing for cyclospora, and that very similar sized and shaped yeasts can be falsely identified as cyclospora.

Mr Pennock submitted that the judge misunderstood the evidence about testing for cyclospora and proceeded on the basis that tests were binary, so that either the regional laboratory’s test was wrong, or the national reference laboratory’s test was wrong. I do not accept this submission. It is clear from the judgment that the judge fully understood the different expert views that were expressed about the significance of the difference in outcome in the two tests. He heard evidence from the Appellant’s expert, Dr Threlfall, as to why the negative test at the national reference laboratory did not mean that the earlier positive test was wrong, but, for the reasons given in the judgment, he rejected it. There was evidence that it was not uncommon for there to be different results in tests for cyclospora in regional laboratories and the national reference laboratory, but this did not mean that the national reference laboratories testing was wrong.

Mr Pennock submitted that the judge failed to appreciate that a single positive test is enough to mean that the presence of cyclospora was “probable” and the purpose of the second test was to turn “probable” to “certain”. With respect, this misses the point. As stated above, the Health Service treats a single positive test, for its purposes, as “probable”, for pragmatic reasons, but that does not mean that the judge was obliged to accept that the test at the regional laboratory was correct.

Mr Pennock referred to scientific papers: the judge was shown some scientific papers in the bundle, but there was no need for him to review them in his judgment. The decision really came down to an evaluation of the evidence, including the live evidence, of Professor Threlfall and Dr Gant. Put another way, there was nothing in the scientific literature which compelled the judge to find in the Appellant’s favour on the cyclospora issue. Mr Pennock also said that the scientific evidence proved on a balance of probabilities that the Appellant had ingested cyclospora. With respect, this is simply an assertion. The evidence of the expert microbiologists was expert evidence, and the judge was entitled to prefer Dr Gant’s evidence.

Mr Pennock submitted that the judge failed to deal with the potential explanations for the different laboratory results. There were two such potential explanations raised with me by Mr Pennock. The first was that cyclospora oocytes were low shedding and so there may have been one or two in the slide that the regional laboratory examined, but none in the slide from the same stool sample that the national reference laboratory examined. This was not put to Dr Gant, and there was no scientific evidence for this proposition. Professor Threlfall’s point was something different, namely that oocytes can degrade or disappear in the course of a week. Mr Pennock also said that there was evidence that the different laboratories used different techniques. In fact, however, Dr Gant said that the techniques used were similar, but, in any event, if different techniques were used, this is not in itself a reason to favour the first test over the second. There was clear evidence that the national reference laboratory was more expert at this type of testing.

I accept that there is a point in the judgment at paragraph 70, at which the judge referred to Dr Gant’s lab and Professor Threlfall’s lab. This was a slip. The national reference laboratory was, in a sense, Dr Gant’s lab, but Professor Threlfall had no connection to the regional laboratory. In fact, Professor Threlfall had been retired since 2010. However, it is clear what the judge meant: the reference to “Professor Threlfall’s lab” was plainly a reference to the regional laboratory which was Professor Threlfall’s lab in the sense that Professor Threlfall was advancing the view that the regional laboratory’s result was to be preferred. In any event, even if, contrary to my view, the judge had thought for a moment that Professor Threlfall had a connection with the regional laboratory, this had no significance for the judge’s reasoning.

Finally, on the cyclospora issue, Mr Pennock said that Dr Gant’s view that national reference laboratory was more expert and experienced than the regional laboratory was an unsubstantiated assertion, without evidence. This is not the case. Dr Gant is an expert microbiologist and the Clinical Director at the hospital at which the national reference laboratory is based. He was very well placed, in light of his expertise and experience, to opine on these matters. He explained his views on this matter.