(Bloomberg Opinion) -- A series of dispatches from America in the age of Covid-19.

My father now knows nine people who have been killed by the coronavirus. He’s 83 and entirely sound of mind and body. He rides his bike many miles every morning around Audubon Park in New Orleans and is as fun to talk to as he was when he was 40. His only response to the news that he and my mother would be confined to the house I grew up in was to call the liquor store and order seven cases of wine.

But now he finds himself watching the annihilation of what is left of his generation. Many of his old high school classmates and business associates and tennis partners live in the Lambeth House, the retirement community of choice for the New Orleans gentry. It’s a peculiar group, with its own customs and language, maybe the only American subculture to use “cocktail” as a verb. Up until a month ago, the few hundred New Orleanians living at Lambeth House cocktailed together nightly, without any idea of the risks they were running. On March 10, the first resident tested positive for Covid-19. At least 52 others now have it, and 13 have died, nine of whom my father knew.

Without more tests it’s hard to say how many people are likely to catch the virus — or how many will die. It seems amazingly well-designed to leap from person to person. People can walk around with it for days and even weeks, carrying the infection wherever they go, without knowing they have it. Young people are especially likely to remain oblivious to their infection, but if an 80-year-old man can feel well enough to cocktail and still be ill enough to give the virus to another 80-year-old man, who can’t?

The surprise, if anything, might be that the virus hasn’t spread more rapidly. “Why don’t even more people have it?” asked Richard Danzig, a national security and bioterrorism expert who served as secretary of the Navy under President Bill Clinton. “Early reports stated that only about 10% of family members of people who fall ill are infected. Possibly the numbers are wrong, but we need to focus on why so many people who are exposed don’t get sick.” The Lambeth House in New Orleans is a case in point. Even now there are a couple of hundred ancients still living there, virus free. How did it miss them?

One possibility — Danzig offered this up the other day at a virtual gathering of pandemic experts — is that the virus has a special need to be projected. “Shorter exposure in some contexts like church events seems to have more impact than prolonged exposure to infected family members at home even when no or few precautions were taken pre-symptomatically,” Danzig wrote to his fellow experts. “I am wondering if singing is the important characteristic of church events (the New Rochelle synagogue, et al), making them a major vector of transmission.”

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Another possibility is that a lot more people than we know — even 80-year-old people — have had the virus but never got sick enough to get themselves tested. That’s what’s so interesting about the simple, one-page letter written last week by two British doctors. Claire Hopkins and Nirmal Kumar, among the country’s most prominent ear, nose and throat specialists, had both noticed the same odd symptom in their coronavirus patients: a loss of the sense of smell. “Anosmia,” it is called, but I suppose they have to call it something.

The inability to smell was the first symptom many patients noticed; in some cases, it was the only symptom the patients noticed. “In the past it was once in a blue moon that we saw patients who had lost their sense of smell,” Kumar told me. “Now we are seeing it 10 times as often. It’s one of the things that happens with this virus.” The British doctors compared notes with doctors from other countries and gathered what data they could. They concluded that roughly 80% of the people who lost their sense of smell would test positive for the coronavirus, and that somewhere between 30% and 60% of those who had tested positive for the virus had also lost their sense of smell.

Those numbers might turn out to be a bit off — maybe even way off. They are a heroic guess, given how little testing has been done. But it’s precisely the scarcity of tests that makes the observation so intriguing, as it offers the possibility of a crude alternative to a test. Lose your sense of smell and you know to isolate yourself, even if you feel great.

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