Toxic air can trigger breathing problems in travellers even during a short stay in cities with high pollution levels, shows a new study done in India, Pakistan and China.

The symptoms could last for at least a week, according to the New York University School of Medicine an analysis of pollution-related coughing and breathing difficulties, and recovery time upon returning home, in healthy, young adults visiting family in cities with consistently high levels of air pollution, including Ahmedabad and New Delhi in India; Rawalpindi, Pakistan; and Xian in China.

Visiting a polluted city reduced lung function by an average of 6% and by as much as 20% in some people, found the study, which was published in the Journal of Travel Medicine.

Air pollution levels remain dangerously high in many parts of the world. New data from the World Health Organization (WHO) shows that 9 out of 10 people breathe air containing high levels of pollutants. Updated estimations reveal an alarming death toll of 7 million people every year caused by ambient (outdoor) and household air pollution.

Researchers analysed six measurements of lung and heart health in 34 men and women travelling abroad for at least a week from the metropolitan New York City area.

“We had several reports that tourists were feeling sick when visiting polluted cities, so it became important for us to understand what was really happening to their health,” said Terry Gordon, a professor at NYU School of Medicine.

The team noted that New York City has relatively low levels of air pollution, in part because of strict regulations, its location on the coast, and weather patterns.

Participants also ranked their respiratory symptoms from one (mild) to five (requiring treatment), reporting a cumulative average symptom score of eight.

People who visited the highly polluted cities reported as many as five symptoms, while those who visited lower pollution cities had fewer or none.

Two patients sought medical attention because of their symptoms, researchers said.The pollution levels of the cities studied did not make a significant difference in the blood pressure of visitors, they said.

All study participants had a normal body mass index (between 21 and 29 for men, and between 18 and 26 for women), and none had preexisting health conditions.

Before embarking on their travels, all were taught how to measure their lung function and heart rate daily using commercially available spirometers, wrist blood pressure monitors, and heart rate sensors.

Researchers then compared the health data against levels of air pollution collected from local government agencies.

They used international standards to categorise highly polluted cities as those having more than 100 microgrammes per cubic metre of particulate matter (PM), or air pollution dust.

Moderate pollution is anything between 35 and 100 microgrammes per cubic metre of PM, and low pollution levels are anything less than that.

“Exposure to high levels of pollution will indeed cause immediate symptoms such as cough, shortness of breath, difficulty in breathing etc. If a person has already had some underlying condition such as asthma, the exposure could further aggravate the symptoms,” says Dr GC Khilnani, former head of pulmonology, All India Institute of Medical Sciences.

Although participants gradually returned to normal health, researchers said there needs to be more follow-up research to know if there were long-term effects, or if longer stays would influence the pollution impact.

“Though there will be short-term symptoms, still there’s not enough evidence to show how damaging the exposure can be in long-term,” said Dr Khilnani.

Gordon suggests that those visiting highly polluted cities should consider wearing masks or consult a doctor prior to travel if they have pre-existing respiratory or cardiac health difficulties, and to consider avoiding travel during certain months. For instance, farmers burn their fields during the winter months in New Delhi, raising levels of pollutants in the city.

Air pollution, measured in particulate matter, in Delhi was about three times the levels in Beijing in 2016, last year’s air pollution analysis from World Health Organisation (WHO) showed. Beijing was one of the most polluted megacities in 2012.

World Health Organisation’s New Global Data and Comprehensive Estimates on Air Pollution 2018 showed India’s most polluted cities in terms of PM2.5 (figures in ug/m3) data available are:

  • Kanpur – 173
  • Faridabad – 172
  • Varanasi – 151
  • Gaya – 149
  • Patna – 144
  • Delhi – 143
  • Lucknow – 138
  • Agra – 131
  • Muzaffarpur – 120
  • Srinagar – 113