NEW DELHI: Chikungunya cases in Delhi have shot up to 423, a massive rise in the figure released by civic authorities, who had reported just 20 cases till last week.

According to a municipal report released today, 423 cases have been diagnosed in the national capital till August 27.

Safdarjung Hospital has reported nearly 250 cases till August 29.

"Chikungunya cases have spiked in the city. We are getting more and more patients with its symptoms. Till August 29, our hospital has reported 246 cases," Medical Superintendent of Safdarjung Hospital A K Rai said.

At the AIIMS laboratories, which get blood samples from Delhi and other parts of the country, 362 samples were tested positive for chikungunya during July to August 20.

"Out of 133 samples sent to our labs, 83 were tested positive in July and this month till August 20, out of 502 samples, 279 tested positive for chikungunya," Department of Microbiology at AIIMS, Lalit Dar, had earlier said.

The South Delhi Municipal Corporation (SDMC) which compiles the vector-borne disease cases report on behalf of all civic bodies, had pegged the total number of cases till August 20 at 20.

Chikungunya is a viral illness and its symptoms are similar to those of dengue, which include high-grade fever, severe joint pain, muscle pain and headache and joint swelling.

It also causes rashes in patients but is not a threat like dengue in which there is a risk of bleeding due to abrupt fall in platelet count.

The sudden spike in chikungunya cases in Delhi and several other parts of north India, has come nearly 10 years after a big outbreak of the mosquito-borne disease across the country.

In 2006, over 13 lakh suspected chikungunya fever cases were reported across the country, according to National Vector Borne Disease Control Programme (NVBDCP).

This year till July 28, 9,990 suspected cases of the disease have been recorded, with Karnataka reporting 7,591 cases.

Health experts have attributed the rise to a possible "evolution" in the virus that carries this disease and change in weather factors like humidity.

"The disease is caused by the same aedes aegypti mosquito which causes dengue but the difference is that dengue virus has four strains while chikungunya has only one," NVBDCP Director Dr A C Dhariwal said.

"The joint pains last longer compared to dengue cases and especially elderly people find it extremely difficult. Though, people should not worry as it not a life-threatening disease like dengue," Dar said.