"Till last year, I used to take an inhaler once a day. But this year, doctors have asked me to take it thrice a day, thanks to the pollution levels which have only got worse. In the last few days, I can feel congestion inside my chest," said Singh, who works as an HR professional in a private firm in Gurgaon.

Singh's condition is symptomatic of the respiratory and other health-related problems in the capital this winter. Doctors said that they have witnessed an increase in the number of cases of respiratory illness this year. Cases of viral infection, cough, sneezing, respiratory tract infection and Chronic Obstructive Pulmonary Disease (COPD) have also gone up this year.

"The number of cases of respiratory illness have gone up by 20 per cent. This is the worst phase for those who have prolonged illnesses. Even cases of viral fever have gone up while those having a history of asthma and COPD are at their worst. Our out-patients department (OPD) is witnessing a large number of patients," said Dr JC Suri, Professor and Head of Pulmonary Medicine at Safdarjung hospital.

The problem has been made worse for patients with the onset of smog. A mixture of fog and air pollutants, smog has been especially harsh on those having a history of respiratory illness, and on children and heart patients who are advised to take special care this year. But doctors say that they are not just getting cases of respiratory illness; cases of sudden cardiac arrest and viral fever are also going up this winter.

"Pollution levels have suddenly increased in the last few days, and, as a result, cases have started to come earlier, as compared to last year. We expect that the level of pollution will be higher this year, which will have an adverse affect on people's health," said Dr SP Byotra, senior consultant, Internal Medicine, Sir Ganga Ram Hospital.

The Air Quality Index (AQI) prepared by US embassy in Delhi gives a better idea of just how bad pollution levels are in the capital. The AQI, which provides data from the embassy and consulate air quality monitors, along with additional data from the Centre and local government-monitoring stations — in New Delhi, Chennai, Hyderabad, Kolkata and Mumbai — showed levels of 527, 459, 458 and 420 at RK Puram, ITO, Anand Vihar, and Siri Fort, respectively.

These levels are classified as hazardous as any reading above 150 is considered unhealthy, with the range 351-500 being classified as 'hazardous'. "This can lead to serious aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and the elderly and respiratory problems for the general public," said a doctor.

A Centre for Science and Environment (CSE) report last year said that air pollution kills 10,000-30,000 people every year.