Fever: how it is assessed here, and why

Most people here arrive on day three or four

Before the timetable, a fact about this practice that changes how to read it. Patients in Cooch Behar do not typically present on day one. The average is three to four days into the fever, and by then most have already taken paracetamol, an antibiotic bought over a shop counter, and something for “gas”. Many have first been seen by a rural practitioner closer to home — which for much of this district is the nearest available medical contact, and is a fact about access rather than a criticism of anyone.

Two consequences follow, and they are the reason this page is written the way it is.

First, the debate about whether to test on day one is largely theoretical here. By the time someone reaches this clinic they are usually at day three or four, which is exactly the point at which a blood count and a malaria test become informative. So the answer to “why are you testing me now when my neighbour was told to wait?” is usually that the neighbour came on day one and you came on day four.

Second, and less obviously: the antibiotic already taken changes what the tests can show, and the word “gas” can hide something dangerous. Both are dealt with below.

Why the first two days usually need no tests

This is the part patients find hardest to accept, and it is worth explaining rather than asserting. Most fevers in the first 48 hours are self-limiting viral illnesses, and testing that early produces two kinds of useless result: the tests that will eventually be positive are often not yet positive, and the tests that are positive may be measuring an old infection rather than this one. ICMR's guidance for community-onset acute undifferentiated fever in adults is explicit about day 1 and day 2 — defer investigation and antimicrobials.^[1]

There is one exception, and it is absolute. Suspected malaria is tested at the first visit, on the first day, because malaria can deteriorate faster than a wait-and-see approach allows. The national malaria guidelines put it as a requirement: all clinically suspected malaria cases should be investigated immediately by microscopy and/or rapid diagnostic test.^[2]

The other thing that overrides the timetable is a danger sign. Those are listed at the end of this page, and they are the part to read first if you are unwell now.

What is actually ordered, and on which day

The staged sequence below is ICMR's, and it is worth knowing that it is expert consensus rather than trial-proven — no study has established day 3 as an optimum. It is not arbitrary, though. It tracks when tests actually become informative: dengue NS1 is useful from day 1 but dengue IgM only from about day 5; blood culture yield is highest early but paired cultures only make sense once a bacterial illness is plausible; scrub typhus IgM is unreliable in the first few days.

Two competing thresholds sit alongside this and are worth stating, because they are stricter rather than looser. Malaria, as above, is tested on day 1. And the Indian dengue guideline treats fever lasting more than three days as an indication for admission in the presence of any warning sign, not merely for testing.^[3]

What changes with the season in Cooch Behar

This is where a general textbook stops being useful and local knowledge starts. The differential for a fever in this district in August is not the differential in January.

From the monsoon into late autumn — roughly June to November — the three that must be actively excluded are malaria, dengue and scrub typhus. North Bengal recorded 81 to 90 scrub typhus cases a year in the northern districts between 2018 and 2020, with deaths in each of those years, and Darjeeling has been a recognised endemic focus since 2004.^[4] Dengue is endemic in the region since the 2005 Siliguri outbreak; Cooch Behar district recorded 576 cases in 2019 and neighbouring Alipurduar 2,542.^[4] Japanese encephalitis also belongs on the list here in a way it does not in most of India — the northern West Bengal districts recorded 48 cases with 19 deaths in 2018, declining since.^[4]

In winter the weight shifts to influenza and pneumonia. Worth knowing: India does not have the single winter influenza peak of Europe and North America. Surveillance in rural West Bengal found H1N1pdm09 circulating in the monsoon, respiratory syncytial virus in autumn, and influenza A/H3 and B in winter — two seasons, not one.^[5]

Fever with jaundice is its own pattern, and here the local answer differs from the textbook one. In West Bengal, hepatitis E accounted for 41.8% of acute viral hepatitis against hepatitis A's 17.2% — so in an adult, E is the more likely of the two, and it matters most in pregnancy.^[6]

Scrub typhus: the one that gets missed

If there is a single reason this page exists, it is this condition. Scrub typhus is common, treatable with an inexpensive tablet, and routinely missed — and the reason it is missed is that the textbook description is wrong for Indian patients.

A meta-analysis of 60 studies covering 34,492 acute febrile illness cases put the pooled Indian scrub typhus proportion at 26.4%, and East India at 27.5%.^[7] Series from West Bengal have reported figures from 10% at North Bengal Medical College to 25.3% at Burdwan.^[8] Call it roughly one in four of the fevers that get properly investigated.

Now the part that changes practice. Textbooks describe the eschar — a dark, painless, scab-covered ulcer at the site of the mite bite — as characteristic. In Indian patients it is present in only about 29% of cases: 28.5% pooled across 83 studies and 11,471 patients, with individual studies ranging from 0% to 74%.^[9] In North Bengal specifically one paediatric series found 19.9%.^[10] The reasons given are that eschars form in the groin, axilla, perineum and under the breast where nobody looks, that they are harder to see on darker skin, and that they heal before the patient presents. So the eschar is looked for carefully — it is diagnostic when found — but its absence excludes nothing at all.

Two further points on scrub typhus, both corrections of things widely repeated. First, mortality: the figure of 40 to 45% for untreated scrub typhus circulates constantly and comes from pre-antibiotic Japanese series. A review of 89 studies covering 19,644 patients put the median untreated case fatality at 6%.^[11] Treated early, it is low single digits. Second, the dictum that failure to improve within 48 hours of doxycycline argues against the diagnosis: time to fever settling with correct treatment ranges from 12 to 96 hours, and the original data behind the 48-hour rule showed fever clearing within three days in 7 of 7 patients at one site but only 5 of 12 at another.^[12] A slow response is not evidence against scrub typhus. Because delay in starting treatment is the main modifiable cause of death, ICMR explicitly permits empirical doxycycline where scrub typhus is suspected and the malaria and dengue tests are negative.^[1]

Malaria here is mostly vivax, and that changes the test

India as a whole is Plasmodium falciparum-majority. West Bengal is not: across 76,320 cases over ten years, 72.6% were P. vivax and 27.3% P. falciparum.^[13] That single fact has a practical consequence, because rapid diagnostic tests are much better at falciparum than vivax — a twelve-site Indian survey of 10,290 participants found sensitivity of 95% for falciparum but only 83% for vivax mono-infection.^[14] A negative rapid card does not exclude vivax malaria in this district, which is why a smear is still examined rather than skipped.

Treatment differs by species too, and this is not interchangeable. Vivax needs chloroquine plus a fourteen-day course of primaquine to clear the liver stages and prevent relapse — the fourteen days are the part people stop early, and stopping early is why the fever comes back three months later. Falciparum in West Bengal is treated with artesunate plus sulfadoxine-pyrimethamine; the artemether-lumefantrine regimen is reserved for the seven north-eastern states, and West Bengal is not among them.^[2] Primaquine cannot be given in pregnancy, to infants, or in G6PD deficiency.

Dengue: which test, and when

Timing decides which dengue test means anything. NS1 antigen is detectable early — around 90% sensitive on day 1, falling to 84% by day 3 — while IgM antibody is only 5% sensitive on day 1, rising to 41% by day 3 and becoming reliable from about day 5.^[15] So NS1 in days 1 to 5, IgM from day 5 or 6, and in the day 4 to 6 window ideally both. IgM also persists for over 60 days, so a positive IgM alone does not prove that this fever is dengue.^[3]

Something worth knowing about the test you may have had elsewhere. The national dengue guideline states plainly that the programme does not recommend the use of RDTs for diagnosis and guiding the management of dengue fever cases, because their accuracy is largely unvalidated, false positives are common, and performance varies from batch to batch.^[3] The inexpensive dengue card available across the district is not a programme-endorsed test. A properly performed NS1 or IgM ELISA is.

And the treatment point that saves lives: paracetamol only. Aspirin, ibuprofen and diclofenac are avoided in suspected dengue because they add platelet inhibition and gastric injury to a condition that already lowers platelets.^[3] This is consensus rather than trial-proven, but the reasoning is sound and the alternative is safe.

Typhoid: why the Widal test is not relied on

The Widal test is probably the most over-used investigation in Indian outpatient fever practice, and the problem is not that it is useless but that it is uninterpretable. Across sixteen studies its specificity ranged from 13.8% to 98%.^[16] A test whose specificity might be 14% or might be 98% cannot tell you anything about an individual patient, and in a population where typhoid is endemic and many people have been vaccinated or previously exposed, a single raised titre is close to meaningless. ICMR's guidance for enteric fever does not mention Widal at all; its diagnostic pathway is blood culture.^[1]

Blood culture is better but far from perfect — roughly 61% sensitive against a composite reference standard.^[17] So a negative culture excludes very little.

What actually determines whether it grows is worth stating, because the received wisdom is wrong. It is widely said that Indian blood cultures are negative because the patient took an antibiotic first. For bacteraemia in general there is truth in that — a trial of 325 patients found positivity falling from 31.4% to 19.4% after a single dose.^[24] But for enteric fever in India specifically, the largest dataset available — 5,703 suspected episodes in Vellore, a quarter of whom had already taken antibiotics — found no significant effect of prior antibiotics on whether the culture grew. The dominant factor was the volume of blood sent.^[25] About 15 mL brings sensitivity close to bone marrow; under 3 mL reduces recovery materially, and 2 to 5 mL is what laboratories are commonly handed.^[17]

So the antibiotic you took before coming is not the reason the culture may fail. Filling the bottle properly is what matters, and that is a fixable thing rather than a reason not to try.

The resistance picture has inverted in a way that surprises people trained twenty years ago. Fluoroquinolones — ciprofloxacin, ofloxacin — are effectively finished: pooled resistance in Indian Salmonella Typhi is 82%, and a 2021–2024 surveillance series across eight sites including Kolkata found only 0.7% of isolates ciprofloxacin-susceptible.^[18] Meanwhile the old multidrug resistance to ampicillin, chloramphenicol and cotrimoxazole has collapsed to near zero, so those drugs have come back into use. Ceftriaxone-resistant and even carbapenem-resistant strains have now been reported from Indian centres, though they remain uncommon.^[19]

Why an antibiotic is often not the answer

This is the conversation that takes the longest and matters most. ICMR states it in one sentence: no antibiotics are required for the majority of patients with acute febrile illness without an obvious clinical diagnosis.^[1]

What actually happens is different. In a study of 1,000 acute febrile illness patients in rural India, 8.3% had taken an antibiotic before arriving, 31.3% received one at the outpatient visit, and acute viral illness accounted for almost half of all antibiotic use — azithromycin most often.^[20] Of those who obtained further antibiotics afterwards, 73% got them from informal providers.

An antibiotic given for a viral fever does not shorten it. It does raise the chance that the next infection, in you or in someone else in Cooch Behar, does not respond — which is how ciprofloxacin stopped working for typhoid. Where there is a specific indication, an antibiotic is prescribed without hesitation and for the full course. Where there is not, the honest answer is that the fever needs a diagnosis or a few more days, and both are better than a prescription.

What happens if nothing is found

Sometimes nothing is found, and it is better to say so than to invent a label. In the best Indian multicentre study of acute fever — seven hospitals, six states, 1,564 patients, with PCR and research-grade serology — about 36% had no cause identified.^[21] Of those in whom a cause was found, malaria accounted for 17%, dengue 16%, scrub typhus 10%, bacteraemia 8%, leptospirosis 7% and chikungunya 6%.

Two things follow. Most people with an unnamed fever recover regardless, which is genuinely reassuring rather than a dodge. And the same study is a caution about how multi-test fever panels are read: apparent double infections on serology panels were largely cross-reactivity and background positivity rather than genuine co-infection. A panel reporting three positives usually means one illness and two artefacts.

Fever that persists past two to three weeks is a different problem with a different list — tuberculosis, lymphoma, connective tissue disease, endocarditis, occult abscess — and it is approached separately rather than by repeating the acute panel. The formal definition of fever of unknown origin is a temperature of 38.3 °C or above for at least three weeks with no diagnosis after appropriate investigation, and even now up to half of such cases are never explained.^[22]

The word “gas”, and why it is worth being careful with

“Gas” does a great deal of work in this district. It is the word patients reach for to describe almost any discomfort between the collarbones and the hips, and most of the time it means exactly what it sounds like. But it is also the word used for two things that are not gas at all, and both matter here.

The first belongs to this page. Abdominal pain is the first item on the WHO dengue warning-sign list.^[23] A patient in September, four days into a fever, with new upper abdominal pain, who takes an antacid and waits, has done a reasonable-sounding thing at the single most dangerous moment of a dengue illness — because that pain is one of the signs that means hospital, and it arrives at just the point when the fever is settling and everyone has relaxed. If you have a fever and the stomach starts hurting, that is not a reason to take something for gas. It is a reason to be seen the same day.

The second is not about fever but is worth saying here because the word is the same: chest discomfort is very often described as gas or acidity, and sometimes it is neither. The reasoning behind that, and why relief from an antacid does not settle the question, is on the chest pain page.

Danger signs: when not to wait for an appointment

These override everything above. If any of them applies, go to a hospital emergency department or call 108 rather than booking a consultation.

ICMR's severity markers for adult fever are three, and they are the cleanest triggers to remember: confusion or altered consciousness, a systolic blood pressure below 90 mmHg, and a breathing rate above 24 per minute.^[1] Add to those: inability to keep fluids down, repeated vomiting, a fit, neck stiffness, reduced urine output, or breathlessness at rest.

In suspected dengue, the WHO warning signs are abdominal pain or tenderness, persistent vomiting, fluid accumulation, bleeding from the gums or nose or in the stool, lethargy or restlessness, an enlarged liver, and a rising haematocrit with falling platelets.^[23] But the one to hold on to is simpler and is the thing patients most often get wrong: in dengue the dangerous phase is when the fever comes down, usually somewhere between day 3 and day 7. Feeling worse as the temperature settles is not recovery going slowly. It is the warning.