Children with asthma are more likely to be admitted to hospital in September than any other month, new figures have shown.
Hospital admissions for under-16s were 58% higher in September 2009 than the monthly average for the year, according to data for England from the NHS Information Centre.
The same thing happened in the previous year, in September 2008, when admission rates were more than double the monthly average.
Experts are unsure what lies behind the increase and have called for further investigation.
Data was analysed for the 12 months from May 2009 to April 2010.
Each month, on average, there were 2,320 hospital admissions for asthma among children under the age of 16.
But, in September 2009, there were 3,670 admissions among under-16s - a 58% rise. Of these, 2,090 were for children aged five and under.
For the 12 months from May 2008 to April 2009, the average under-16 admission figure was 2,380.
In September 2008, the figure was 4,820 (103% higher), of which 2,780 cases were for children aged five and under.
Hospital admissions among older age groups do not follow the same pattern.
Asthmatics are less likely to be admitted when they are older, with admission rates among older age groups peaking in October or December.
Tim Straughan, chief executive of the NHS Information Centre, said: “Although provisional, these figures provide a useful insight at a national level into the admissions passing through our hospital doors in England, and also into possible shifts in trend during the different seasons.
“These figures appear to highlight September as a hotspot for asthma admissions among our very young children, which may prompt possible investigation as to why this may be.”