Red flags first, then what actually separates them, then what to test. This tool does not diagnose — in the first week the honest answer is often "test all three".
Malaria is never excluded on clinical features here. Falciparum malaria can kill within days, the three pictures overlap heavily in week one, and co-infection is real. In an endemic setting, test every patient with undifferentiated fever — and repeat if negative and suspicion persists.
Decision-support only. Each arm follows its own guideline — WHO 2025 for malaria, WHO 2009 and DEAG Punjab for dengue, MMIDSP 2022 for typhoid. This tool suggests what to test and what not to miss; it does not make a diagnosis and does not replace clinical judgement.
✓ Clinically reviewed by Dr Syed Usama Hussain, MBBS, BSc · 05 Aug 2026.
Step 1 · Does this qualify as undifferentiated fever?
MMIDSP 2022
Any patient presenting with fever with no clear focus of infection in an endemic setting, for more than 3 days should be suspected to have typhoid fever. It is important to rule out malaria, dengue and other possible causes of febrile illness.
Step 2 · Red flags — check these before anything else
WHO 2025 malaria · WHO 2009 dengue · MMIDSP 2022
If any of these are present, the question is no longer which illness it is. Tick everything that applies.
Severe malaria
One or more of the following, in the absence of an identified alternative cause and in the presence of P. falciparum asexual parasitaemia. WHO Guidelines for malaria (13 August 2025) — definition of severe falciparum malaria
Severe dengue
Any one of these defines severe dengue. WHO Dengue Guidelines 2009, Figure 1.4
Complicated typhoid
Manage at a tertiary care centre. MMIDSP Typhoid Management Guidelines 2022
Step 3 · Features that shift the odds
probability shifters — not decisions
These narrow the differential. They do not settle it. Overlap between the three is substantial in the first week, and a patient may have more than one.
Favours Dengue
Abrupt high fever, often with severe myalgia and retro-orbital pain
Rash
Positive tourniquet test
Leukopenia
Falling platelet count with a rising haematocrit
Deterioration around defervescence rather than at peak fever
Residence in or travel to a transmission area — including within Pakistan
Anaemia
Splenomegaly
Jaundice
Step 4 · What to test, in what order
the actual deliverable
1
Malaria rapid diagnostic test and/or thick and thin blood films
Always, first, regardless of how dengue-like or typhoid-like the picture looks. It is fast, cheap, and the one that kills quickest if missed. Repeat if initially negative and suspicion persists.
WHO Guidelines for malaria (13 August 2025) — definition of severe falciparum malaria
2
Two sets of blood culture — BEFORE antibiotics
Optimal before starting antibiotic therapy, and also in patients already on antibiotics who are not responding. Automated cultures can flag positive as early as 4 hours, with identification and susceptibility in the following 48 hours — and susceptibility is what determines the whole typhoid treatment path.
MMIDSP Typhoid Management Guidelines 2022
3
Full blood count with platelet count and serial haematocrit
A rising haematocrit with a concurrent rapid fall in platelets is the WHO laboratory warning sign in dengue. The trend matters, not a single value. Leukopenia supports dengue; bicytopenia is a typhoid complication marker.
WHO Dengue Guidelines 2009, Figure 1.4
4
Dengue NS1 antigen and/or serology, by day of illness
Interpret against the day of illness — NS1 is highest early, antibodies appear later.
WHO Dengue Guidelines 2009, Figure 1.4
Do not rely on Widal or TyphiDOT. “Positive serological tests (such as Widal and TyphiDOT) are not recommended for diagnosis of enteric fever and are not included in case definitions of typhoid. Serological tests should never be ordered or relied upon to diagnose or rule out enteric fever.”
Step 5 · Things that change management here
Pakistan-specific practice points
P. vivax predominates in Pakistan, and this matters for severity: WHO defines severe vivax and knowlesi malaria exactly as for falciparum but WITH NO PARASITE DENSITY THRESHOLDS. A vivax patient with jaundice or severe anaemia is severe malaria without needing to meet the falciparum parasite counts.
Fever defervescence in typhoid is prolonged and may take 5–7 days. Do not rush to change antibiotics — and do not read a persisting fever on day 3 as a failed diagnosis.
Dengue deterioration classically happens as the fever settles, not at its peak. A patient improving symptomatically on day 4 may be entering the critical phase.
Co-infection happens. A positive test for one does not exclude the others.
Frequently asked questions
A patient has had fever for 4 days — is it dengue, typhoid or malaria?
Often you cannot tell on clinical features alone in the first week, and that is the honest answer. Certain features shift probability — retro-orbital pain, rash and thrombocytopenia toward dengue; stepwise fever and abdominal symptoms toward typhoid; rigors and paroxysms toward malaria — but overlap is substantial and co-infection occurs. Test rather than guess: malaria film or RDT first, two blood cultures before antibiotics, and a full blood count with serial haematocrit.
Can malaria be excluded clinically?
No, and this tool will not let you. Falciparum malaria kills within days, and its early presentation overlaps completely with dengue and typhoid. In an endemic setting, test every patient with undifferentiated fever, and repeat the test if it is negative and suspicion persists.
What defines severe malaria?
WHO lists impaired consciousness (GCS under 11 in adults, Blantyre under 3 in children), prostration, more than two convulsions in 24 hours, acidosis, hypoglycaemia below 2.2 mmol/L, severe anaemia, renal impairment, jaundice with high parasitaemia, pulmonary oedema, significant bleeding, shock, and parasitaemia above 10%. Any one, in the absence of an alternative cause, defines severe malaria.
Does severe vivax malaria need a high parasite count?
No — and this matters in Pakistan where P. vivax predominates. WHO defines severe vivax and knowlesi malaria exactly as for falciparum but with no parasite density thresholds. A vivax patient with jaundice or severe anaemia is severe malaria without needing to meet the falciparum parasite counts.
Which test should be done first?
The malaria test. It is fast, cheap, and the diagnosis that kills quickest if missed. Then two sets of blood culture before any antibiotic is given, because susceptibility determines the entire typhoid treatment path in a country with XDR strains.
Is the Widal test useful?
No. MMIDSP states that Widal and TyphiDOT are not recommended for the diagnosis of enteric fever, are not included in the case definitions, and should never be ordered or relied upon to diagnose or rule out enteric fever. Blood culture is the standard.
The fever has not settled after 3 days of antibiotics — is the diagnosis wrong?
Not necessarily. Fever defervescence in typhoid is prolonged and may take 5 to 7 days. The guideline explicitly warns against rushing to change antibiotics, and notes that appetite and general condition often improve before the fever does.
The dengue patient is improving as the fever settles — is that reassuring?
The opposite. Deterioration in dengue classically happens around defervescence, not at peak fever. That transition is the critical phase, and it is when plasma leakage occurs.
Clinically reviewed by Dr Syed Usama Hussain, MBBS, BSc
MBBS, BSc — active medical practitioner in Pakistan. Graduated from Federal Medical & Dental College, Islamabad (2021) and completed a one-year clinical internship at the Pakistan Institute of Medical Sciences (PIMS), Islamabad (2022).
Sources
WHO Guidelines for malaria, 13 August 2025 — definition of severe falciparum, vivax and knowlesi malaria
WHO Dengue: Guidelines for Diagnosis, Treatment, Prevention and Control, 2009 — Figure 1.4
Dengue Expert Advisory Group (DEAG), Government of the Punjab — Dengue GCP Guidelines 2020
Medical Microbiology & Infectious Diseases Society of Pakistan — Typhoid Management Guidelines 2022
Background reading — why the first question is not "which of the three", the severe-vivax rule with no parasite threshold, and the three traps that catch people in week one: fever in Pakistan.