Did the English smoking ban stop 90,000 children get...

"90,000 children spared illness by smoking ban," reports the Daily Mail. This impressive-seeming statistic is based on research looking at how many under-14s ended up in hospital with respiratory infections in the years before and after the July 2007 smoking ban in England and Wales.

Researchers analysed data on more than 1.6 million children who were admitted to NHS hospitals for respiratory infections – excluding asthma cases – between 2001 and 2012. To put this into context, children are unlikely to be admitted to hospital with a mere cold or sniffle – these are likely to be children very ill with bronchitis, pneumonia, laryngitis or tonsillitis.

The researchers calculated the rate of admission for any respiratory tract infection reduced by 3.5% immediately after the introduction of the smoking ban. It then continued to reduce by 0.5% each year.

The biggest immediate reduction in admissions was for lower respiratory tract infection (such as pneumonia), which reduced by 13.8%.

While this study can't prove the smoking ban definitely caused the drop in the numbers of children needing hospitalisation, the research appears robust and we have confidence that the findings are likely to be accurate. The researchers accounted for potential confounding factors, including the introduction of the pneumococcal vaccine in 2006.

And while this study shows the smoking ban is associated with around 11,000 fewer hospital admissions for respiratory tract infections in children a year, it cannot tell us the potential wider benefits of the smoking ban on children's health.

Now is the best time to quit smoking.

Where did the story come from?

The study was carried out by researchers from Maastricht University and Sophia Children's Hospital, both in The Netherlands; Brigham and Women's Hospital in the US; and the University of Edinburgh and Imperial College London in the UK.

It was funded by the Thrasher Research Fund, the Netherlands Lung Foundation, the International Pediatric Research Foundation, and The Commonwealth Fund.

The study was published in the peer-reviewed European Respiratory Journal.

The media reported the study accurately, though some did not point out the limitations of this type of study, in that it cannot prove cause and effect.

The Guardian's figure of 11,000 children a year saved from hospital admissions reflects the estimates in the research. The Mail's figure of 90,000 appears to be an extrapolation of this figure over the eight years since the ban. The research only went up to 2012, so this figure can't be verified, but the Mail's headline claim is unlikely to be wildly inaccurate.

What kind of research was this?

This was an observational study looking at the number of admissions for respiratory tract infections in children before and after the smoking ban was introduced in July 2007. This type of study is useful when it is not feasible to perform a randomised trial, though it cannot prove cause and effect.

The scientists knew secondhand smoke exposure was a major risk factor for respiratory tract infections. However, no-one had yet studied the direct impact of the smoking ban in England on children's health in this way.

What did the research involve?

The researchers used the Hospital Episode Statistics database to collect data. They looked at the monthly number of hospital admissions for children aged 0 to 14 in England and Wales with respiratory tract infections between January 1 2001 and December 31 2012.

The researchers calculated the rate of admissions according to the number of admissions divided by the number of children at risk of admission to account for any changes in the number of children in the population over time.

The rate of admission to hospital before and after the smoking ban was introduced on July 1 2007 was compared, taking some potential confounding factors into account.

The results were adjusted using standard statistical analysis to take into account:

age group (0 to 4, 5 to 9 and 10 to 14 years)
gender
socioeconomic deprivation
level of urbanisation
region
introduction of the pneumococcal vaccine in 2006

What were the basic results?

There were 1,660,652 admissions for acute respiratory tract infections among 0 to 14 year-olds during the study period. Most occurred in children up to age four (85%), and admission was more likely with increased deprivation.

Overall, respiratory tract infection admissions reduced by 3.5% immediately after the introduction of the smoking ban (admission rate -3.5%, 95% confidence interval [CI] -4.7 to -2.3%). The rate continued to reduce each year thereafter by 0.5% (admission rate -0.5%, 95% CI -0.9 to -0.1%).

The biggest immediate reduction in admissions was for lower respiratory tract infections (such as pneumonia) – these were reduced by 13.8% (admission rate -13.8%, 95% CI -15.6 to -12%).

The smoking ban was associated with an estimated 54,489 fewer hospital admissions over the next five years.

How did the researchers interpret the results?

The researchers concluded that, "The introduction of national smoke-free legislation in England was associated with ~ [around] 11,000 fewer hospital admissions per year for RTIs in children."

They say their research demonstrated "an immediate reduction in lower RTI admissions, and a more gradual, incremental reduction in upper RTI admissions".

Conclusion

This observational study found an association between the introduction of the 2007 smoking ban in public places in England and Wales, and a reduction in children's hospital admissions for respiratory tract infections.

The study included data on a large number of admissions for respiratory tract infections in children, using nationwide official hospital statistics to gather this information. This gives us confidence in how well these findings may be generalisable because it limits selection bias.

The researchers took several potential confounding factors into account when analysing their results, including:

the introduction of the pneumococcal vaccine for children in 2006
seasonal variations
temperature
levels of air pollution

They only included children up to the age of 14 in an attempt to limit the effect of adolescent first-hand smoking. A cut-off point had to be used, though recognising there will be children under the age of 14 who smoke.

However, this study has limitations because of its design. As it is a "before and after" type of study, there may have been other factors that changed that may have influenced the results.

Hospital admissions may have reduced over time as a result of improvements in the treatments available for respiratory tract infections in children – for example, at home, through a pharmacist, GP or A&E services, or because of preventative measures.
Private hospital admissions were not included and their use may have changed over the study period. However, this is believed to be less than 1% of total admissions.
Admissions for children with asthma were excluded so they did not bias results, but children with other conditions that increase their risk of respiratory tract infections were included. The number of children with these conditions – such as cystic fibrosis – may have changed over the study period.
Epidemics such as H1N1 (swine) flu in 2009 will have increased the number of admissions. The authors say that despite this increase in infections in the "after" stage of the study, there was still an overall reduction in the number of admissions for respiratory tract infections in children after the smoking ban.

The study could not directly measure the impact the smoking ban had on people smoking in their homes or cars, which is one of the main sources of secondhand smoke for children.

However, the authors cited several credible studies that found the number of smoke-free homes increased significantly after smoking bans.

Overall, this study shows the smoking ban is associated with around 11,000 fewer hospital admissions for respiratory tract infections in children a year.

If you still haven't given up smoking, now is as good a time as any and you can get free help to quit from the NHS.