Much of our understanding of each virus comes from hospital-based studies. People in this environment, whether admitted (inpatients) or presenting but being allowed back home (outpatients), represent the "tip of the iceberg" of the disease spectrum. The pointy end. The most severe cases.
We may make the assumption that the viruses circulating in the community are represented by what's happening in a hospital environment - or vice versa. But how often have we tested that? Do we know if there is a lag or lead time? Does it differ by climate? Could we go further and perhaps use those numbers to predict what the burden of disease in hospital will be this "season"?
And then there's the ongoing testing issue. Research dollars generally do not fund epidemiology. Certainly not ongoing epidemiology. Even big hospitals and private testing labs cannot afford the personnel and cost of testing all respiratory samples for all "likely" viral pathogens, all the time. "Likely" having been defined with the caveats above.
And so our epidemiology data have holes. Big ones. We read of complaints about some countries not being able to identify a viral/bacterial cause (not that a POS lab test does prove cause) of pneumonia or encephalitis...but many patients in more "developed"countries also leave hospital without ever being attached to a lab-confirmed positive result. We could reduce that, even if we could not specifically treat them.
And therein lies another issue. We test for some viruses based on historical precedent - do those precedents accurately stand up today? Do we even have the data to answer that? If you are a health professional, have a look at what your local testing lab offers - does it cater for the most likely causes of ARI or just what's been used before?