When my dad was 9 years old he had whooping cough. Then it went it away for 55 years. Then, slowly, it began to creep back, as he got older and his immune system became less aggressive. And I think this is a common story for almost any virus: once you get it, you have it for life, but for most of your life, while your immune system is strong, the virus will remain repressed. But once you get older, those viruses start coming back.

We know of many viruses that can resurface, decades later. Shingles is perhaps the most common, something like 25% to 33% of people eventually get shingles (according to the CDC, 96% percent of the USA population has the herpes zoster virus).

And of course, we now know that many things that used to be thought of as a natural part of the aging process are in fact caused by bacteria:

gum disease

stomach ulcers

heart disease

There is also evidence that most back pain is caused by bacteria (according to the CDC, 30% of the USA population shows signs of exposure to spinal meningitis).

There is also the theory that certain forms of dementia are driven by bacteria. (Dementia onset following a bout of pneumonia is a common story.)

I think this man's story fits into the ordinary story of a man getting older and his immune system getting less aggressive.

In terms of cost/benefit analysis, it is worth noting, if we could find a general way to boost the immune system, the benefits would apply to thousands of illnesses, including all of the most common ones. Research on any one disease is less likely to yield the sort of wide benefits that boosting the immune system would offer. Such research (to boost the immune system in a general way) might seem a bit far fetched, but I think it justified by the large benefits it could yield.