If December and the first half of January were spent battling influenza, my time in Brussels and Luxembourg was all about pretending to do battle with cholera. Mann's title Death in Venice has three aspects - the death of Aschenbach himself, the uncanny personification of death in the strange figures who accost the writer during his reckless sojourn (a theme which the dying composer amplified to chilling effect in the opera), and the cholera which is rampaging through the city. It's often been thought that Mann was exaggerating the extent of the cholera on the 1911 trip which inspired the book, but in fact the last great cholera pandemic did reach Europe, Italy in particular, killing 116 people in Venice, 873 in Naples and 6,146 in the country as a whole. It inspired a government cover-up that threatened non-compliant doctors with jail and falsified the historical record.

Hanseatic, wealthy Hamburg (Thomas Mann was from neighbouring and Hanseatic Lübeck) had suffered a shocking outbreak only two decades earlier, 8,616 people dying of the disease in 1892. But cholera, over and above the historical account, is ideal for Mann's purposes in Death in Venice. Chillingly swift and undignified in its impact upon the human body, it is the master metaphor of the novella, its power as a metaphor only enhanced by the fact - one I took on board in the past month - that Mann is resolutely ambiguous as to whether Ashchenbach actually dies of the disease. "Disease," as Mann was to write in The Magic Mountain, "is only love transformed," and Aschenbach's sickness is really of the soul.

Britten and his librettist, Myfanwy Piper, brilliantly intensify this by getting Aschenbach to emphasise his thirst, his thirst for change at the beginning of the opera-terrible thirst being, of course, one of the early symptoms of cholera. At this stage of course, there can be no question that he actually has the disease, but the lines are being blurred, in the same way that the smeary low tuba sonorities at the end of the act confuse and muddy the declaration of his secret love. Ambiguity is a feature of all Britten's operas, as he himself acknowledged, and it is a strangely unoperatic quality, one of the keys to his modernity, and unsettling. What I have yet to rationalise is how as an actor one can characterise that ambiguity. Does Aschenbach contract cholera? Do I need to know?