The long-awaited rodent section of the English House Condition Survey has just been published. Although there are few real surprises, it establishes many links pest control experts have suspected for decades. Cathy Savage reports

If 1996 seems a while ago in human terms, it's hard to imagine just how long it's felt in rat years. Nonetheless, although many of the rodents who contributed to the data have since gone to the great mousehole or sewer in the sky, the rodent survey element of the 1996 English House Condition Survey has finally been published.

Rodent infestations in domestic properties in England has an initial shock value with an apparent drop in rodent infestations. However this fall is debatable and beyond that the report should hold few surprises for those working in pest control. What is most important about the document though is that it finally makes the link between infestations and housing fitness with one coherent dataset.(1) It makes clear what pest control experts and housing specialists have known for a long time - unfit dwellings and dwellings in areas with substantial problems, such as dereliction, litter, vacant properties and scruffy gardens, have a higher rate of rat and mouse infestation. It also shows for the first time the link between pets, livestock and infestation.

In many ways the information is a significant improvement on previous surveys, which were based on notifications to local authorities or random sampling of premises with little or no information about the properties affected. However, the survey is far from perfect - which is demonstrated by the "drop" in infestations and the scepticism with which this has been greeted. The survey suggests total rates of infestation which are less than half of those given in the last national survey.(2) It claims a rate of 1.8 per cent for mice, 0.4 per cent for indoor rats and 1.7 per cent for outdoor rats. Nice though it might be to believe that rodents are on the wane, the difference seems likely to be one of methodology and practice rather than a lack of rats and mice.

"One of the problems with this survey is in terms of making comparisons," explains Adrian Meyer, a rodent consultant who helped draw up the questions for the EHCS during his days at the Central Science Laboratory, and also worked on previous rodent surveys.
"The drop is likely to be a case of different people doing things in different ways. Previous surveys were done using methods developed in the 1970s, and the results compared favourably with the data collected in the 1970s. The methodology had been drawn up by the Rodent Research Laboratory and surveys were carried out by specialist pest controllers.
"This one used different methods and was carried out by EHOs and surveyors. I think it's likely that the higher level found previously is the more reliable guide to levels of infestation."
Mr Meyer's view is backed up by the fact that questions asked about rodents in the 1993 EHCS suggested a significantly smaller problem than the national rodent survey conducted in the same year.(2)
Overall the EHCS data suggests two general forms of infestation. One is the rural model - with infestation of older properties on large plots typically in rural areas, often with pets or livestock in the gardens. The other is urban - with the infestation of properties that are less than satisfactory in terms of fitness, situated in areas of high-density housing with substantial problems.

The survey shows a clear trend of increase in infestations as fitness declines, with infestations in unfit dwellings double those in satisfactory dwellings. "It's good that it makes the link between unfitness and rat infestation, though not surprising at all," says Steve Battersby, rodent expert and researcher at the Robens Centre for Public Health. "Poorer areas tend to have older housing, older drains, more defects, poorer environments, more litter and more harbourage; that's what poorer areas are like and it's no surprise that they have higher infestations as a result. What we need now is for any rodent strategy to be linked with any housing strategy, and also related conditions that affect infestation."
One of the major factors picked out in the survey was drains. "Despite the difficulties of relating individual fitness characteristics to infestations, there was some indication that outdoor rat infestations were related to blocked drains," says the survey report. "This is of particular interest given the possible link between above ground rat problems and rats living in sewer systems."
Although it warns against assuming a direct link, the data does back up what experts have been saying for a long time.

"We've been arguing this for years," says Mr Battersby, who is also a leading member of the Campaign for the Renewal of Older Sewerage Systems. "The thing is it's not just unfitness when it comes to drains. There are issues of disrepair not sufficient to make a dwelling unfit but that need attention." He would like to see additional information gathered - about the age of drainage systems, the materials they are constructed from and any past history of problems. Something Mr Meyer was happy to see in black and white was the link between animals and rodent numbers. The presence of pets or livestock in gardens roughly trebled the level of infestation (from 1.5 per cent to over 4.5 per cent for mice, 0.3 per cent indoor rat infestation to more than 1 per cent and almost 1.5 per cent outdoor rat infestation to 6 per cent). The geographical pattern was mixed, but it appeared to show rat infestations to be least common in the north east and mouse infestations to be low in the south-east and east of the country.

Generally rates of infestation tended to be higher in rural locations and higher in older properties - which of course also tend to be in a poorer state of repair. The widest plots also seemed more prone to infestation, perhaps linked to their age and location. The data shows a pretty low rate of treatment, with only about 35 per cent of rat infestations and about 55 per cent of mouse infestations being dealt with. This is a cause of concern for Mr Battersby. "It confirms what was found in 1993, that a substantial number of infested properties aren't being treated," he explained. "Even taking the lower rates of this survey - which suggests about 370,000 infested dwellings and comparing that to the number of treatments reported to CIEH (roughly 130,000), there is still a big shortfall and that is a problem."

Where the infestation was being treated, traps tended to be favoured for mouse control, where poisons were more common for rats, although this may show nothing more than the trend for professional control to be brought in more often for rats and professionals using poisons more than amateurs.
It seems that for as many linkages that have been made, there are still many questions unanswered, and not necessarily for lack of data. "MAFF could have used the data from the EHCS in much more detailed ways than they actually did," claims Mr Battersby. "The fundamental problem that they haven't got pest control specialists working on the information."
The positive outlook though, is that Rodent infestations in domestic properties in England does represent a foundation to build on, and, by drawing some obvious conclusions, it has taken a long overdue leap towards joined-up thinking on rodent control.

1. Rodent infestations in domestic properties in England, a report arising from the 1996 English House Condition Survey, MAFF, London. Website: www.maff.gov.uk
2. Meyer A, Shankster A, Langton SD and Jukes, G, National commensal rodent
survey 1993, Environmental Health Journal 103 pp 127-135.