An Eosinophil Count From a Routine Physical, and a War That Ended 50 Years Ago
A Vietnam veteran's routine annual physical turns up incidental eosinophilia and, on closer questioning, a fifty-year-old exposure history and a rash he's been told for decades is probably an allergy. The debate is whether to treat presumptively for Strongyloides now, or wait on a serology test whose sensitivity, while good, isn't perfect.
W.T., a 74-year-old retired machinist, came in for the same Medicare wellness visit he's had every year since he turned 65 — nothing about today felt different to him until his physician started asking follow-up questions about a CBC drawn for unrelated fatigue workup two weeks ago, one that came back with an eosinophil count of 9%, higher than anything in his chart going back a decade. Asked directly, he mentions, almost as an aside, a faint rash that shows up on his trunk every few months, comes and goes within a day, and that two different doctors over the years have called "some kind of allergy" without ever pinning down to what. He also mentions, only because his physician asked specifically about foreign travel and deployment history, that he served a tour in the Mekong Delta in 1970 and 1971, and remembers wading through rice paddies with wet boots for weeks at a time — a detail that hadn't occurred to him as medically relevant in fifty-five years.
The rash he's describing, migratory and serpiginous, is a reasonable match for larva currens, the characteristic skin finding of chronic strongyloidiasis, and the eosinophilia and the deployment history both fit the same picture: chronic Strongyloides infection can persist for decades via an internal autoinfection cycle, entirely without ongoing exposure, and stays clinically silent or minimally symptomatic in most people who carry it. The stakes of missing it are not symmetric with most parasitic infections travel medicine screens for — if he is ever immunosuppressed later in life, steroids for a COPD flare, chemotherapy, anything that suppresses cellular immunity, a chronic low-grade infection like this can convert to hyperinfection syndrome, whose reported mortality runs from roughly 15% to nearly 90% and sits at the top of that range when nobody knew the infection was there to look for. His own numbers are what make that a live question rather than a textbook one: 9% eosinophilia is the only abnormality he has, and in hyperinfection the eosinophil count characteristically collapses rather than climbs, so the finding that brought him in is a marker of the chronic phase he is in now, not a warning that would still be visible if he crossed into the phase everyone is afraid of. Serology, per CDC's own account, runs roughly 88-98% sensitive but falls off in exactly this kind of chronic, low-burden infection; stool ova-and-parasites testing is genuinely poor for this organism given how intermittently larvae are shed.
A test with real sensitivity, and a wait that might not matter
Send the serology and wait for it. It's one blood draw, reasonably sensitive, and results in a week or two — we can start ivermectin the moment it's back. And a positive result does something empiric treatment never would: it puts a permanent, documented flag in his chart that matters enormously if he's ever immunosuppressed decades from now and nobody in that room remembers to ask about a deployment from 1970.
He's asymptomatic enough today that a two-week wait costs him essentially nothing clinically. I'd rather have the documentation than skip straight to treatment.
I don't disagree that documentation has real value. What worries me is what happens if the serology comes back negative — which it can, even in a genuine chronic infection, given how low-burden this can run after fifty years — and this visit's momentum doesn't carry forward. He's 74, this was an incidental finding on an unrelated fatigue workup, and I don't want a falsely negative test to be the reason he's never treated at all.
Ivermectin's safety profile is excellent, and the asymmetry here is stark: hyperinfection syndrome, if it ever happens, kills a large share of the people who get it, and most of them are people nobody knew were infected. That asymmetry is worth more to me than the two-week wait saves us.
I'd send the serology — the documentation argument is real and worth having regardless of what today's decision ends up being. But I want to name the actual gap in both of your positions: a single negative result in a chronic, low-burden infection like this one shouldn't be treated as fully reassuring, and neither of you has said what happens if it comes back negative and he still has that rash next spring.
Send the test, but write the plan down now: if it's negative and he's still symptomatic at any point, treat anyway rather than letting one imperfect result close the question. That protects the documentation value without betting everything on a test we already know isn't perfectly sensitive.
Agreed: serology sent today, with an explicit plan written into the chart that a negative result does not close the question if his rash or eosinophilia recur — treatment would proceed regardless at that point.
Not fully resolved: the travel medicine physician would still have preferred treating today, unconditionally, rather than waiting even two weeks, and said so again at the end of the visit, specifically citing the risk that an elderly patient's incidental finding doesn't always get the structured follow-up a younger, more engaged patient's would. The infectious disease physician held that the documentation value of a formal result, combined with the fallback plan the group agreed to, adequately addressed that risk without needing to skip testing altogether. W.T. himself, asked directly, said he'd rather know for certain what the test shows — the deciding vote, in the end, wasn't clinical.