Fever in Adults: What It Means and When to Worry
A fever is a body temperature of 38 C (100.4 F) or above, and it is the immune system working rather than an illness in itself. Most fevers in adults come from a viral infection and settle within three days on paracetamol, rest and fluids, with no antibiotic and no blood test. In Pakistan a fever lasting more than three days — or one with severe headache behind the eyes, a rash, repeated vomiting, or much less urine than usual — should be tested for dengue, typhoid and malaria rather than treated with another course of antibiotics. Get emergency help the same hour for a fever with confusion or drowsiness, a stiff neck, difficulty breathing, a rash that does not fade when pressed, bleeding from the gums or nose, a fit, or a fever in anyone on chemotherapy or with a suppressed immune system.
Diabetologist & General Physician · MBBS
What counts as a fever
Normal body temperature is not a single number. It sits between roughly 36.1 C and 37.2 C (97 F to 99 F), runs about half a degree lower in the early morning than in the late afternoon, and is slightly higher in the second half of a woman's menstrual cycle. A fever is a temperature of 38 C (100.4 F) or more. Between 37.3 C and 37.9 C is usually described as a low-grade temperature, and it is common in the day or two before a fever proper appears.
Fever is a deliberate act by the body. The brain raises its own thermostat in response to chemical signals released during , and the higher temperature makes it harder for many and to multiply while speeding up the immune response. This is why bringing the number down does not make the illness shorter — it only makes you more comfortable while your body does the work. It is also why the shivering comes first: your body is trying to reach the new, higher setting.
Measure with a digital thermometer under the tongue with the mouth closed, or under the arm, adding nothing to the reading — modern digital thermometers are calibrated for where they are placed. Do not measure within fifteen minutes of a hot or cold drink. Forehead strips and hand-on-the-brow are not accurate enough to make a decision on.
What causes fever in adults here
Roughly three fevers in four are viral and self-limiting. What makes a Pakistani fever different from the one in an imported leaflet is the group that follows: dengue after the monsoon, typhoid all summer, malaria in rural and riverine areas, and tuberculosis behind any fever that has run for weeks with weight loss and night sweats.
| Likely cause | Season | Typical extra clues | First test |
|---|---|---|---|
| Viral upper respiratory infection | All year, peaks in winter | Sore throat, blocked nose, cough, body aches; better by day three | None needed |
| Dengue | Post-monsoon, roughly August to November | Severe headache behind the eyes, bone and muscle pain, rash, falling count | Dengue NS1 antigen plus a |
| Typhoid (enteric fever) | Summer, and after unsafe water or street food | Fever climbing step by step over days, abdominal discomfort, constipation more often than diarrhoea | Blood culture, taken before antibiotics |
| Malaria | After the monsoon, mainly rural and riverine districts | Fever with shaking chills then drenching sweats, often every second or third day | Malaria rapid test or a blood film |
| All year | Burning on passing urine, going often, pain in the flank or lower back | and urine culture | |
| Chest infection or pneumonia | Winter | Cough with coloured sputum, breathlessness, sharp chest pain on breathing in | Chest |
| Tuberculosis | All year | Fever for weeks, night sweats, weight loss, cough lasting more than two weeks | Sputum GeneXpert and chest |
How long is too long
Day one to three is the ordinary window. Most viral fevers peak on the second day and are settling by the third, and testing in that window often produces nothing useful — a dengue antibody test taken on day one is frequently negative even in someone who has dengue. From day four the question changes: a fever that has not begun to settle by then deserves blood tests rather than a second guess. A fever lasting more than two weeks, with weight loss or night sweats, is investigated differently again, and tuberculosis is high on that list in Pakistan.
How it is diagnosed
Most of the diagnosis is the history: how many days, how high, what pattern, what came with it, where you have been, what you ate, who else at home is unwell. Where tests are needed, the usual first set is:
- A . A falling count with a rising haematocrit suggests dengue; a high count points towards a bacterial infection; a low one is common in dengue and typhoid alike.
- A dengue NS1 antigen test in the first five days, and dengue IgM after that.
- A malaria rapid diagnostic test or a thick and thin blood film, repeated if the first is negative and suspicion is high.
- A blood culture for typhoid, which must be taken before any antibiotic is started or it will grow nothing.
- where there are urinary symptoms, and a where there is or right-sided abdominal pain.
- A chest for cough, breathlessness or chest pain.
- C-reactive protein, which rises in bacterial infection but is not specific enough to decide an antibiotic on its own.
Treatment
For an ordinary viral fever the treatment is fluid, rest and paracetamol, and nothing else helps. is for comfort: it will typically bring the temperature down by one to one and a half degrees and let you sleep, and that is its entire job.
Antibiotics do nothing at all for a viral fever. Taking one "just in case" does not shorten the illness, does add diarrhoea and rash to it, and does contribute to — which in Pakistan is not an abstract worry: extensively drug-resistant typhoid has been circulating here since 2016 and has already removed several once-reliable oral options from use. Where an antibiotic is genuinely needed, the choice depends on the organism and on local resistance patterns, and it is a prescriber's decision.
What you can do at home
- Drink more than feels necessary — water, lassi, soup, fresh lime with a little salt and sugar, or if there has also been vomiting or diarrhoea. Fever raises fluid loss by about 10 per cent for each degree above normal.
- Check that you are still passing pale urine several times a day. Dark, scanty urine is the earliest sign of .
- Dress lightly and keep the room comfortable. Piling on quilts to "sweat it out" traps heat and makes the fever worse.
- Sponge with tepid water if you want to, not cold water and never ice, which causes shivering and drives the temperature back up.
- Rest properly. Sleep is not lost time in an infection.
- Eat what you can manage. Appetite returning is one of the most reliable signs of recovery.
- Keep away from mosquitoes while you are ill in dengue season — a person with dengue infects the mosquitoes that bite them, and that is how a household outbreak starts.
When to see a doctor
See a doctor if a fever has not started to settle by the end of the third day, if it returns after having gone, if it is above 39 C and not responding to paracetamol, or if it comes with a rash, jaundice, persistent vomiting, severe headache or pain passing urine. Anyone with diabetes, kidney disease, liver disease, a suppressed immune system, or who is pregnant should be seen earlier rather than waiting the three days. And go straight to an emergency department, without waiting for an appointment, for any of the warning signs listed near the top of this page.
Common questions
Still not sure what to do?
Reading about a symptom only goes so far. A doctor who can ask you questions and examine you will get further in ten minutes than any article can.
