July 11: The season of viral afflictions is here, striking almost every household in town in the form of a bout of common cold, influenza or the more serious dengue fever.

The spurt in health problems in the middle of the wettest July in years is no coincidence. Significant rainfall almost every day since the previous week has created conditions ideal for viruses and vectors to proliferate, public health experts said.

Clinics and outpatient departments of government and private hospitals have been swamped by patients with one or more of these symptoms - fever, sore throat, cough, sneezing and lethargy. The majority of them have infections of the upper respiratory tract, a common occurrence at this time of the year.

In some cases, tests have revealed the cause of fever to be dengue, which is spread by the Aedes aegypti mosquito. "Given the current weather conditions, we should take the first few dengue cases as a warning sign," infectious diseases specialist Amitabha Nandy said.

The maximum temperature in Calcutta had been in the range of 36 to 37 degrees Celsius till the middle of June, but started dropping thereafter as rainfall picked up. Rainy and humid weather with moderate temperature create perfect conditions for the spread of viruses and vectors. "Like all other organisms, viruses struggle to survive in extreme temperature. Their survival rate increases when they are inside a vector or in the air," Nandy said.

The typical symptoms of viral fever are temperature up to 103 degrees Fahrenheit, accompanied by a runny nose and cough. The number of patients with these symptoms have jumped since the rainy spell started in July. This kind of fever subsides within five days or so.

According to pulmonologist Ajay Sarkar, people on immuno-suppressive drugs and those with COPD and asthma are predisposed to upper respiratory tract infections at this time.

"Children are vulnerable too because they do not have as many antibodies in their system as adults do," paediatrician Apurba Ghosh said.

Air-borne diseases like the common cold or influenza spread through droplets when someone already afflicted sneezes or coughs. Doctors advise patients to follow "cough etiquette" so that the virus does not spread.

Most of the dengue cases reported so far have been from the Dum Dum area. Three members of a family living near Dum Dum station have tested positive this week.