Swine flu and invasive aspergillosis.

Medscape sent round some articles at the start of the week. One in particular, which consisted of two case reports and a discussion, caught my interest. The case report was from respiratory specialists at Columbia University and the University of California.

Two patients, both men, contracted H1N1 influenza (swine flu) last year and ultimately succumbed to respiratory and systemic complications of that disease. In each case:
- acute respiratory distress syndrome (ARDS) developed rapidly;
- influenza was not diagnosed immediately;
- high doses of corticosteroids were given as methylprednisolone to treat the ARDS;
- the influenza virus was complicated by invasive aspergillosis.

In each case, bronchoscopy was performed within the first few hours of intubation, and evidence of aspergillus, a fungus, was detected. In one this was clearly invasive infection, evident on biopsy samples from the airway.

Now aspergillus in the lungs is becoming a bit of an interest of mine. The article I read today confirms that there is increasing recent evidence that patients with COPD are at risk of invasive aspergillosis. Prevalence of this problem, however, in the massive population of patients with COPD is probably very low. There is understood to be a very high mortality rate in such patients (upwards of 95%). For a number of reasons, documentation of the extent of the problem is limited. A good review of this issue from 3 years ago is given here.

In the cases discussed, it was suggested that the impact of influenza virus on airway and systemic defence mechanisms (reduced white blood cells, reduced movement of ‘cilia’ – fine hairs on the airway walls) combined with the steroids, which are a disaster for airway immune defence, created a great environment for aspergillus to get a toehold.

New information for me was the availability of some blood tests to assist in the diagnosis of invasive aspergillosis. A serum galactomannan assay has been available since around 2006 in the USA and for longer in Europe. It has moderate diagnostic accuracy for invasive aspergillosis. Bronchoalveolar lavage galactomannan has been demonstrated to be quite sensitive and specific for invasive aspergillosis in the lungs.

I am not sure that this assay is available in Australia, and will need to find out. As (swine) flu season is upon us we should probably have a reasonable index of suspicion that the aspergillus isolates we grow in cultures – particularly of our hospitalized patients- may not simply be contaminants. Perhaps invasive aspergillosis, which many of us have considered to be unlikely to occur outside of the profoundly immunosuppressed, is on the rise. Further evaluation with CT chest and bronchoscopy should be considered, and considered early in patients who are unwell.

Andrew