Link found between low pollution levels and hospital admissions in rural areas
22 April 2009 by Tom Marshall
Air pollution in rural areas has been linked to a rise in the number of patients admitted to hospital suffering from severe lung complaints.
A patient receives emergency oxygen treatment for breathing difficulties
Links between high levels of air pollution and hospital admissions in large towns and cities are widely known. This new research - the first major study based on rural populations - connects much lower levels of pollution with hospital admissions.
The researchers based at the University of East Anglia in Norfolk examined 1050 hospital admissions in the rural county of Norfolk, UK, during a 13-month study. All 1050 patients had been clinically diagnosed with chronic obstructive pulmonary disease (COPD), sometimes used as an umbrella term for severe lung complaints like chronic bronchitis and emphysema, which results in restricted airflow to the lungs.
The team found that relatively slight increases in carbon monoxide, nitric oxide, nitrogen dioxide and other oxides of nitrogen were associated with more hospital admissions. An increase of ten microgrammes per metre cubed of nitrogen dioxide led to a 20 per cent increase in the odds of a patient needing hospital treatment for COPD.
Dr Andrew Jones, senior lecturer at the University of East Anglia's School of Environmental Sciences, said, "The data were being collected to monitor treatments for the disease, but we realised we could use it to look at the links between admissions and low level pollution."
"Previous research in large cities shows when air pollution levels are high, symptoms worsen and we see more hospitalisations," says Jones.
But in three hospitals in rural Norfolk, the team found relatively small increases in pollution levels led to more hospital admissions.
Unsurprisingly, the researchers found pollution concentrations much lower than in cities, with the exception of ozone, which is usually higher in rural areas. Even so, the researchers found no link between admissions and either ozone levels or particulate levels.
Curiously, there was a spike in admissions on Monday.
"We think this related to people delaying seeking medical attention," says Jones.
It seems people put off going to hospital even when their symptoms are serious. Assuming their condition will improve they hold off seeing a doctor. When the weekend hits, it is common then to wait until Monday before seeking treatment.
The researchers used data from the NERC's British Atmospheric Data Centre to look at the weather conditions - temperature, wind speed and rainfall - at the time of the study.
The paper, published in the Journal of Epidemiology and Community Health, contributes to the debate on whether there are threshold levels below which pollution is benign.
"There's a lot of talk in the area of respiratory research about the idea of thresholds," says Jones. "Some research suggests the relationship between pollution levels and exacerbation of the disease is not linear.
"We have tried to find out if there was a pollution threshold where patients in more rural areas did not show symptoms with air pollution."
But the answer seems to be no. Even very low pollution levels can increase the number of hospital admissions.
The study centred around the small city of Norwich with only 160,000 inhabitants. The catchment area for the three hospitals was a radius of thirty to forty miles around the city so many of the patients will have come from rural areas. Unlike larger cities, Norwich has few sources of wide-scale industrial atmospheric pollution making it a good place for this kind of research.
"What we can learn from this is that patients need to be aware of pollution levels," says Jones. "The government could develop an early warning system where people can check pollution levels and modify their behaviour as a result."
More research is required to confirm the results and see if a threshold can be found below which air pollution levels do not lead to hospital treatment.