Below is how to think about a lingering flu-like illness, which blood markers add information, and where blood work stops being useful.
Most lingering flu-like illness in adults comes from ordinary causes rather than a fungal infection from the soil. Common respiratory viruses account for the largest share, and the cough and tiredness they leave behind can outlast the fever by weeks. Short sleep, a heavy training block with no deload, high stress, regular alcohol, under-eating relative to training load and seasonal allergy all deepen that tired, foggy, achy feeling. Some medicines also contribute, so ask your prescriber before assuming anything else is going on. Life stage matters too, since recovery capacity and sleep quality shift across adulthood.
None of those causes show up as a single abnormal lab value. They show up as a pattern over weeks, which is why a history of the last month usually explains more than any one test.
Valley fever belongs in the conversation when there has been dust exposure. The fungus behind it lives in dry soil, and spores become airborne when soil is disturbed by wind, digging, construction, farming, landscaping or off-road driving, then reach the lungs when they are inhaled 1. Exposure is not the same as illness. Research suggests that most infections cause no symptoms at all or only a mild illness that settles without anyone identifying the cause 1.
When symptoms do appear, they generally begin one to three weeks after the spores are inhaled, and the primary illness usually looks like community-acquired pneumonia, with cough, fever, chest discomfort, night sweats, headache and marked fatigue 2. Joint and muscle aching is common enough that the illness has long carried a nickname referring to rheumatic pain 3. Skin findings such as erythema nodosum, the tender red lumps that often appear on the shins, and erythema multiforme are associated with early coccidioidomycosis and are among the clues that point away from an ordinary viral illness 7.
The honest summary is that the symptoms overlap almost completely with far more common conditions. That overlap is exactly why a clinician uses context, examination and targeted testing rather than symptoms alone.
Three blood tests do most of the work, and only one of them is specific to this infection. Two general markers describe the immune and inflammatory pattern, and a dedicated antibody test looks for the fungus itself.
| Marker | Why it is linked to this illness | What a result can and cannot tell you |
|---|---|---|
| Eosinophils | A white blood cell subtype that can rise in allergy, parasitic illness and some fungal infections. Peripheral eosinophilia is associated with coccidioidomycosis in a portion of patients 3. | A raised count flags an immune pattern worth explaining. It cannot name the cause, because allergy, asthma, eczema, parasites and some medicines also raise it. |
| C-Reactive Protein | A liver protein that rises with systemic inflammation and falls as inflammation settles, which gives a rough sense of how active an illness is. | Shows how much inflammation is present, not where it sits or what started it. A normal result does not exclude a localised lung process. |
| Coccidioidal antibody testing (clinician ordered) | Looks for antibodies the immune system makes against the fungus, and it is the usual route to identifying the infection 2. | Can support identification and, followed over time, can reflect how extensive the illness is. A negative result early in the illness does not rule it out 6. |
Typical lab reference ranges for the two general markers look like this.
| Marker | Typical lab reference range | Units |
|---|---|---|
| Eosinophils, absolute count | 0.0 to 0.5 | ×10⁹/L |
| Eosinophils, percentage of white cells | 0 to 5 | % |
| C-reactive protein, standard assay | less than 5 to 10, depending on the assay | mg/L |
| C-reactive protein, high sensitivity | less than 3 | mg/L |
These are typical lab reference ranges and they vary by lab, age and sex. Read your own report against the range printed on it.
A high eosinophil count can be one clue among several, but on its own it never identifies the cause of an illness. Eosinophils are white blood cells that sit mostly in tissue rather than blood, and the blood count reflects how strongly a particular arm of the immune response has been switched on.
The link to this infection is real but partial. Peripheral blood eosinophilia is associated with coccidioidomycosis and is one of the laboratory findings that can prompt a clinician to consider it in someone with pneumonia that is not behaving as expected 3. It is more a prompt than an answer, since plenty of people with the infection have an entirely ordinary eosinophil count, and the marker can also rise in illness confined to the lungs.
A great deal else moves this marker. Seasonal allergy, asthma, eczema and chronic sinus disease push it up. Parasitic infections push it up. Some medicines do too, so ask your prescriber about anything you take regularly before reading much into a single count. Eosinophil counts also vary through the day, which is one reason a repeat test weeks later often reads differently from the first.
So the practical sequence is this. The observation is a count above the printed range. The possible meaning is an immune response involving allergy, parasites or certain infections, which can include this one. The next step is a conversation with a clinician about exposures, timing and symptoms, and a repeat measurement rather than a conclusion drawn from one number. You can read more about what the count covers on the Eosinophils marker page.
C-reactive protein is checked because it gives a quick, cheap read on how much systemic inflammation is present right now. The liver produces it in response to inflammatory signalling, levels climb within hours of an acute insult, and they fall again as the process settles, which makes the marker useful for tracking the arc of an illness.
It is useful here for a simple reason. Pulmonary coccidioidomycosis usually presents in the same way as community-acquired pneumonia, with cough, fever and chest symptoms that no one can distinguish from a bacterial pneumonia by appearance alone 5. A markedly raised inflammatory marker tells a clinician that something active is going on and is worth pursuing with imaging or specific testing, rather than waiting it out. A falling value over following weeks tells a different story from one that keeps climbing.
What it cannot do is point to a location or a culprit. C-reactive protein rises with dental infection, a skin infection, a recent injury, autoimmune conditions and flare-ups of chronic inflammation. It also drifts upward with higher body fat and smoking, and it can tick up for a day or two after unusually hard training, which matters if you tested the morning after a long session.
The sequence again runs observation, then meaning, then next step. A raised value is an observation that inflammation is active. Possible meanings range from a short-lived infection to something more persistent. The next step is to pair it with symptoms, examination and, where the history includes dusty exposure and a cough that will not clear, specific testing arranged by a clinician. The C-Reactive Protein marker page covers how the standard and high-sensitivity versions differ.
Antibody testing looks for proteins your immune system makes in response to the fungus, and it is the main way the infection is identified in practice 2. No needle finds the fungus itself in blood. The test finds your response to it.
In plain words, laboratories look for two classes of antibody. One appears early in the illness and fades within weeks. The other develops later and persists for longer, which is why the two together help place where someone sits in the course of the illness. A screening test is usually run first, and a positive or unclear screen is followed by confirmatory methods that measure how much antibody is present rather than only whether it is there.
That quantity matters. Studies indicate that antibody levels followed over time track the course of the illness, and that higher levels are associated with more extensive disease, including spread beyond the lungs 6. This is why a clinician may repeat the test rather than relying on one reading.
Timing is the main trap. Antibodies take time to appear, so a test drawn in the first days of symptoms can come back negative in someone who truly has the infection, and repeat testing is sometimes needed before the picture becomes clear 6. Antibody responses can also be blunted in people with weakened immunity, the same group in whom research suggests the infection is more likely to spread beyond the lungs to skin, bone or the lining of the brain 2.
Antibody testing is not the only tool. Chest imaging, examination of material coughed up or sampled from the lung, culture and tests that look for fungal components may help when antibody results are inconclusive or when someone is unwell enough to need an answer quickly 4. Which of those is appropriate is a clinical judgement, not a self-service decision.
A completely normal blood panel does not rule this infection out, and it does not explain most lingering fatigue either. Eosinophils can sit squarely in range in someone who is infected, and C-reactive protein can be modest in a mild or resolving illness. Neither marker is specific, so a normal pair narrows nothing in particular.
General blood work also cannot localise a problem. It will not show a patch of inflammation in one lung segment, nor distinguish a residual lung nodule left behind after this infection from other causes of a nodule, which is a recognised reason people end up having imaging and sometimes sampling to settle the question. Imaging answers questions that chemistry cannot.
Then there is the long list of fatigue causes that no blood test captures at all. Accumulated sleep debt, untreated sleep-disordered breathing that needs a sleep study rather than a blood draw, low mood, chronic stress, an under-fuelled training block and the slow tail of a recent viral illness all produce the same complaint. A reader with a clean panel and persistent exhaustion has not been told nothing. They have been told to look outside the blood.
Finally, timing cuts both ways. A test drawn too early can miss a developing antibody response, and a single snapshot of any inflammatory marker describes one morning rather than a trend. Serial measurement usually beats a single heroic panel.
Some symptoms are worth prompt attention rather than a wait-and-see week. Contact a clinician promptly for breathlessness at rest or on mild exertion, chest pain, coughing up blood, a fever that persists beyond about a week, or a cough that has gone on longer than three weeks without improving.
Seek urgent care for a severe headache with neck stiffness, confusion, visual change or persistent vomiting, since those point to involvement of the lining of the brain, which is one of the recognised routes this infection can take beyond the lungs. New skin ulcers, draining lumps or nodules, and deep bone or joint pain in one site also deserve prompt assessment, because skin and bone are among the places disease outside the lungs shows itself 7.
Unintentional weight loss, drenching night sweats and progressive weakness are reasons to be seen sooner rather than later. In people with weakened immune systems, including those living with conditions or taking therapies that suppress immunity, the threshold for getting checked should be lower 2. Do not try to settle this yourself, and do not ignore a result that sits outside the standard range because you feel fine.
If you are having thoughts of self-harm, call or text 988 (US) or your local emergency number now.
Eosinophils and C-reactive protein are standard blood tests, and both are included in the FitScript Essential panel alongside the rest of a baseline workup, with membership covering 150+ biomarkers tested per year. Atlas, the AI health advisor, explains what each result means in plain language and shows how values move across repeat draws, which is usually more informative than one reading.
One limit is worth stating plainly. Coccidioidal antibody testing is a specific test ordered and interpreted by a clinician in the context of symptoms and exposure, so it is not something a general wellness panel answers. A baseline panel is useful for describing the inflammatory and immune pattern, and for giving a clinician a reference point from before you became unwell.
This page is educational and is not medical advice. Discuss your results and any treatment with a clinician or licensed provider, and remember that treatment decisions belong to a licensed provider who has reviewed you.
Coccidioidomycosis is the medical name for valley fever, a lung infection caused by breathing in spores of a fungus that lives in dry soil. Many people never feel ill at all. Others develop a cough, fever, night sweats and fatigue that can last for weeks. A clinician confirms it with antibody testing.
The symptoms of valley fever usually look like a flu or pneumonia that will not clear. Common ones are cough, fever, chest discomfort, night sweats, headache, aching joints and deep fatigue. Some people also notice tender red lumps on the shins. Symptoms often begin one to three weeks after a dusty exposure.
Fatigue, cough and night sweats tend to outlast everything else, sometimes continuing for weeks after the fever has settled. Joint and muscle aching can also linger. New skin ulcers or lumps, bone pain, weight loss or a severe headache are different, and they are reasons to contact a clinician without waiting.
You catch it by inhaling fungal spores released when dry soil is disturbed by wind, digging, construction, farming, landscaping or off-road driving. Spending time outdoors in dusty conditions where the fungus lives in the soil raises exposure. Most exposures cause no illness, and many people never know they were exposed.
No. It spreads by inhaling spores from soil rather than from person to person during ordinary contact, so household members are not at risk from someone who is ill. When several people fall ill at once, it is usually because they shared the same dusty exposure, not because they infected each other.
Not on its own. A routine panel can show eosinophils and C-reactive protein, which describe an immune and inflammatory pattern worth explaining, but neither names a cause. Identification needs specific antibody testing, and sometimes chest imaging or a sample from the lung, all ordered and interpreted by a clinician.
Fatigue often outlasts the fever and cough, and it can linger for weeks or longer after the acute illness settles. Returning to hard training too quickly tends to stretch that recovery out. If the tiredness is deepening, or new symptoms appear such as weight loss or night sweats, see a clinician.
See a clinician promptly for breathlessness, chest pain, coughing blood, fever lasting beyond a week, a cough past three weeks, new skin ulcers, bone or joint pain, or severe headache with neck stiffness or confusion. Adults with weakened immune systems should be assessed early rather than waiting for improvement.