The Return of Swine Flu – A Death in the U.S. and Uncertainty

Sadly, the U.S. reported its first death in a 23 month old Mexican toddler visiting in Texas.

Cases have developed in countries on at least five continents over a brief time period. The first death in the U.S. among 64 cases, which is also the first death globally outside of Mexico among 100 or more cases, is difficult to put into perspective with any confidence – especially since the baby came from Mexico. The death of a baby in the U.S. is tragic, but each year we see 36,000 deaths from influenza in our country. Influenza is always serious – even without an exotic strain from another country. We cannot at this time predict the mortality of the Swine flu outbreak, but only put in a range of 0.1% of cases to something higher such as 0.5% (seen in the 1957 “Asian” flu and 1968 “Hong Kong” flu pandemics). A 1% mortality may be worst case scenario and seems unlikely.

If more deaths are occurring in Mexico than the rest of the world, why would this happen? In both the U.S. and Mexico the same virus is attacking the same age cohort – young adults. Then any big differences would be ascribed to differences in patients. Is it possible that patients in Mexico have co-infection with a second virus? Do they have high rates of secondary bacterial pneumonia with Staphylococcus aureus or Pneumococcus? Is the particulate air pollution in Mexico City damaging airways and lungs causing more disease? Do patients have an unusually robust immune response to the virus – the so-called cytokine storm? We do not know the answers to any of these questions, but the key point is this: CDC in concert with health authorities in Mexico should perform sophisticated viral and bacterial studies, and pathology analyses on patients with severe disease and on patients who have died. Our understanding of how to manage this viral infection will be enhanced with such information.

As we prepare ourselves in the U.S. for more illnesses and more deaths from the new Swine flu, it is the uncertainty that is especially challenging. Knowing the cause of severe illnesses and deaths and the true mortality will be of critical importance.