Post-Monsoon Dengue: Why September Can Be a Danger Period

The rains are easing and the skies are clearing, but the mosquitoes are not going away. In many parts of India, dengue picks up just as the monsoon winds down.

The lag effect

Dengue doesn't peak when the rain does. A five-year study from a hill state in northern India found that dengue peaked in October, about two months after rainfall and humidity peaked in August, and the rise continued into November even though the monsoon ended in September. A study at a North Indian hospital found a similar pattern, with cases clustering from August to November and positivity peaking in September and October. 

It varies by region

There is no single national calendar. Across six southern states, transmission peaked mainly between October and December, after the monsoon, though individual states shifted from year to year. In Delhi, dengue has historically peaked in August, September and October, so a quiet start to the year says little about how the season will end. Heavy late rain can make things worse. In one year of delayed monsoon withdrawal, an expert linked the surge in cases to water accumulating from heavy rains that continued well into October. 
south india has no single dengue season it differs across states +2

A daytime mosquito

Dengue spreads through the bite of infected Aedes mosquitoes, which have white markings on the body and legs and are most active during the day. They can breed in relatively small amounts of stagnant water, such as a flowerpot saucer, a cooler tray or a discarded container. 

Know the warning signs

Dengue is not always mild. Warning signs of severe dengue often appear after the fever has subsided, so feeling better is not always a sign of recovery. Watch for severe or worsening abdominal pain, severe weakness, persistent vomiting and bleeding. A person can also catch dengue more than once, and a later infection carries a higher risk of severe dengue. 

What you can do

• Empty and scrub water containers weekly. This includes coolers, buckets, plant trays and tyres.
• Cover water tanks and clear clogged drains around your home.
• Protect yourself in daytime too with repellent, full sleeves and screens.
• Get tested early if fever comes with body ache or severe headache.
• Use paracetamol for fever. WHO recommends paracetamol to reduce fever and pain in dengue. Check with a doctor before taking aspirin or ibuprofen. 
• Rest, drink plenty of fluids, and go to hospital at once if warning signs appear.

Don't let your guard down when the rain stops. The weeks after the monsoon are when stagnant water, humidity and mosquitoes combine, so keep up the checks through November.

Sources: National Centre for Vector Borne Disease Control (NCVBDC) data as reported by The South First; National Journal of Community Medicine; Healthline journal (North India study); Down To Earth; The Quint (citing IMD); New Straits Times (WHO guidance).