Fever during the Mumbai monsoon often creates one immediate question
“Is this dengue, malaria or leptospirosis?”
It is a reasonable concern. Mumbai sees a predictable rise in these infections during and after periods of heavy rain and waterlogging.
In July 2026, BMC surveillance data reported 1,380 malaria cases, 466 dengue cases and 78 leptospirosis cases, all higher than in June. But there is one important message at the outset:
You usually cannot distinguish dengue, malaria and leptospirosis reliably from symptoms alone, particularly during the first few days.
All three can cause fever, headache, body ache, weakness, nausea and abnormalities in the blood count. The patient’s exposure history, day of illness, examination and appropriately timed investigations often provide the real clues.
1. Dengue: Don’t Focus Only on Platelets
Dengue is a viral infection transmitted by infected Aedes mosquitoes.
Common symptoms include:
– Sudden fever
– Severe headache
– Pain behind the eyes
– Muscle and joint pains
– Marked tiredness
– Nausea or vomiting
– Rash
The early phase can resemble several other viral illnesses, malaria and even leptospirosis.
The biggest dengue misconception: “My platelets are falling”
A falling platelet count is common in dengue, but platelets alone do not determine whether
dengue is becoming severe.
Doctors look at the complete clinical picture: blood pressure, pulse, hydration, urine
output, bleeding, hematocrit and, most importantly, warning signs.
Another important point is that dengue can sometimes become more dangerous when the
fever starts coming down.
The critical phase typically occurs around days 3–7 of illness. Warning signs include severe
abdominal pain, persistent vomiting, fluid accumulation, mucosal bleeding, lethargy or
restlessness and a rising hematocrit associated with a rapid fall in platelets.
Therefore:
“Fever has gone, so dengue is over” is not always true.
Avoid aspirin, ibuprofen, diclofenac and similar NSAIDs when dengue is suspected
because of bleeding risk. Paracetamol is generally preferred for controlling fever.
2. Malaria: Fever Does Not Have to Follow a Classic Pattern
Malaria is caused by Plasmodium parasites transmitted through infected Anopheles
mosquitoes.
Many patients expect malaria to always produce the classic sequence of:
Chills → high fever → sweating
Or fever at fixed intervals.
That pattern may occur, but especially early in the illness, malaria can simply present as an
undifferentiated fever.
Symptoms can include:
– Fever
– Chills or rigors
– Headache
– Sweating
– Body ache
– Weakness
– Nausea or vomiting
Both Plasmodium vivax and Plasmodium falciparum occur in India, and either infection
deserves proper assessment. Malaria can occasionally progress to severe illness affecting
the brain, kidneys, liver, lungs or circulation.
WHO recommends confirming suspected malaria using microscopy or a malaria rapid
diagnostic test rather than diagnosing malaria from symptoms alone.
Can the first malaria test be negative?
Yes.
A negative first test reduces the likelihood of malaria but may not always exclude it when
clinical suspicion remains strong.
Repeat microscopy may sometimes be necessary. CDC guidance recommends repeating
blood smears at 12–24-hour intervals, up to three sets, in patients in whom malaria
remains strongly suspected despite an initially negative smear.
The key message for patients is simpler:
Persistent fever deserves reassessment. Do not assume one negative test explains
everything.
3. Leptospirosis: Floodwater Exposure Is an Important Clue
Leptospirosis is different from dengue and malaria because it is a bacterial infection.
Leptospira organisms can be present in water or soil contaminated by urine from infected
animals, particularly rodents. Infection can enter through cuts or abrasions in the skin or
through mucous membranes.
Heavy rainfall and flooding therefore make leptospirosis particularly relevant in Mumbai.
One question can immediately change the diagnostic thinking:
“Did you walk through floodwater recently?”
Symptoms may include:
– Sudden fever
– Headache
– Chills
– Severe muscle pain
– Nausea or vomiting
– Diarrhoea
– Redness of the eyes
– Weakness
Pain or tenderness in the calf muscles and lower back and redness of the eyes known as
conjunctival suffusion are useful clues, but they are not present in every case and should
not be used for self-diagnosis.
Severe leptospirosis can affect the kidneys, liver, lungs, brain and circulation.
Unlike dengue, leptospirosis requires antibiotics. When clinical suspicion is strong,
treatment should not necessarily be delayed while waiting for confirmatory laboratory
results.
How Can Doctors Tell Them Apart?
There is considerable overlap.
Clue| Dengue| Malaria| Leptospirosis
High fever| Common| Common| Common
Severe body ache| Common| Can occur| Common
Chills/rigors| Can occur| Often prominent| Can occur
Pain behind eyes| May occur| Less typical| Can occur
Falling platelets| Common| Possible| Possible
Calf muscle pain| Possible| Possible| Suggestive clue
Red eyes| Possible| Less typical| Suggestive clue
Jaundice| Severe disease| Possible| Important clue
Floodwater exposure| Not diagnostic| Not diagnostic| Raises suspicion
No single symptom or blood-test abnormality reliably separates these three illnesses.
Which Tests May Be Needed?
Testing depends heavily on which day of fever the patient is on.
For suspected dengue, NS1 antigen or molecular testing is useful during the early phase.
Dengue IgM usually becomes detectable around day 4–5 and becomes more useful later. A
negative test performed too early may therefore need clinical reassessment.
For malaria, microscopy and/or an appropriate rapid diagnostic test are used.
For leptospirosis, PCR can be particularly useful early in the illness, while the sensitivity of
antibody testing increases during the second week.
Other investigations may include:
– Complete blood count
– Hematocrit
– Liver function tests
– Kidney function tests
– Urine examination
– Additional tests depending on symptoms and clinical findings
When Should You Seek Urgent Medical Attention?
Do not wait at home if fever is accompanied by:
– Persistent vomiting
– Severe abdominal pain
– Breathlessness
– Bleeding
– Fainting or very low blood pressure
– Confusion or excessive drowsiness
– Seizures
– Reduced urine output
– Jaundice
– Cold or clammy hands and feet
– Inability to drink adequate fluids
– Rapid deterioration, particularly when the fever is settling
Pregnant women, older adults, children and people with significant heart, kidney, liver
disease or other major medical conditions may need earlier assessment.
Not Every Monsoon Fever Is One of These Three
This is another common trap.
Influenza/H1N1, COVID-19, other viral respiratory infections, gastroenteritis, enteric fever
and several other infections can also cause fever during the monsoon. In July 2026,
Mumbai also recorded increases in H1N1 and gastroenteritis.
Starting antibiotics simply because fever has continued for two or three days may therefore
obscure rather than solve the problem.
The Bottom Line
If you develop fever during Mumbai’s monsoon, remember three things:
Don’t diagnose dengue only from a falling platelet count.
Don’t rule out malaria simply because the fever does not follow the “classic” pattern.
And always mention recent floodwater exposure to your doctor because it can
substantially increase suspicion for leptospirosis.
Most importantly, if fever persists, warning signs develop or the diagnosis remains unclear,
reassessment is more useful than repeatedly adding medicines or antibiotics.
In monsoon infections, the right diagnosis often depends not on one symptom or one test,
but on putting together the day of illness, exposure history, examination and changing
laboratory findings.