We found that a range of modifiable risk factors were associated with secondary care-attended falls from furniture, falls on stairs or steps, poisonings and scalds in children aged 0–4 years. Only two modifiable risk factors were associated with secondary care-attended falls on one level in children aged 0–4 years.
TABLE 30 Comparison of the results from the complete-case and multiple imputation analyses for those exposures for which there was a>10% difference (continued)
Exposure Complete-case analysis Multiple imputation analysis % Difference Difference AORa (95% CI) AORa (95% CI) Child left in bath without adult even for a
moment at least some daysc
0.47 (0.30 to 0.75) 0.55 (0.38 to 0.80) 17.1 0.08
Bath run for child by an older child at least
some daysc 0.74 (0.31 to 1.82) 0.92 (0.50 to 1.68) 23.9 0.18
Older child looked after child in the bath at
least some daysc
1.10 (0.63 to 1.93) 0.75 (0.48 to 1.18) –31.5 –0.35
Child not taught rules about things not to climb on in the kitchen
1.66 (1.12 to 2.47) 1.41 (1.02 to 1.93) –15.3 –0.25
Child not taught rules about what to do or not do when parents are cooking using the top of the cooker
1.95 (1.33 to 2.85) 1.68 (1.21 to 2.32) –14.0 –0.27
Child not taught rules about hot things in the kitchen
1.89 (1.30 to 2.75) 1.61 (1.18 to 2.19) –14.9 –0.28
Child not taught rules about what to do or not do when in the bathtub
1.42 (0.85 to 2.37) 1.84 (1.32 to 2.58) 29.9 0.42
Did not use stationary activity centreb
1.22 (0.83 to 1.79) 1.45 (1.03 to 2.04) 18.5 0.23
a Adjusted for confounders as inTable 28. b In the last 24 hours.
Compared with control parents, parents of children who had a fall from furniture were more likely not to use safety gates anywhere in the home (PAF 15%) and, for those with children aged 0–12 months, were more likely to have left them on raised surfaces (PAF 50%), changed nappies on raised surfaces (PAF 34%) and put them in car/bouncing seats on raised surfaces (PAF 12%). Parents of children who had fallen from furniture were less likely to put children aged 13–36 months in car/bouncing seats on raised surfaces (78% reduction in odds). They were more likely not to have taught children rules about things they should not climb on in the kitchen (PAF 16%) and, for those with children aged≥37 months, their children played or climbed on furniture more often (PAF 88%) than control children. Case children who had had a fall from furniture played or climbed on garden furniture less often than control children (26% reduction in odds). Compared with parents of controls, parents of children who had had a fall on one level were less likely not to use furniture corner covers (28% reduction in odds) and less likely not to have rugs/carpets firmly fixed to the floor (23% reduction in odds). The association with rugs/carpets firmly fixed to the floor varied with the number of adults in the household. Households with one adult in which children had had a fall on one level were more likely not to have rugs/carpets fixed to floors than control households (PAF 18%), whereas households with two adults in which children had had a fall on one level were less likely not to have rugs/carpets fixed to floors than control households (31% reduction in odds).
Compared with parents who kept safety gates closed, parents of children who had fallen down stairs or steps were more likely not to use safety gates on stairs (PAF 21%) or to leave safety gates on stairs open (PAF 24%) than parents of controls. Compared with control households, the odds of not using a safety gate on stairs and of leaving the gate open appeared to be particularly high in families with children aged 0–12 months (PAF 18% and 46%, respectively) and the odds of leaving safety gates open appeared to be high in families who used baby walkers (PAF 44%). Families with children who had fallen down stairs or steps were more likely than controls not to have carpeted stairs (PAF 5%) or not to have a landing part-way up their stairs (PAF 18%). They were also more likely to consider their stairs not safe to use (PAF 5%) or in need of repair (PAF 5%). They were less likely than controls to have tripping hazards on their stairs (23% reduction in odds) or not to have handrails on all stairs (31% reduction in odds). Compared with controls, families with no adults in paid work whose children had fallen down stairs or steps were more likely to have taught children rules about carrying things down stairs and leaving things on stairs (56% and 73% reduction in odds of not teaching rules, respectively). Compared with controls, single adult families whose children had fallen down stairs or steps were more likely to have taught children rules about leaving things on stairs (67% reduction in odds of not teaching rules) and to not have carpeted stairs (PAF 26%).
Compared with parents of controls, parents of children who had had a poisoning were more likely not to store medicines at adult eye level or above (PAF 15%), not to store medicines safely (locked away or at adult eye level or above) (PAF 16%) and not to put medicines (PAF 20%) or household products (PAF 11%) away immediately after use. They were also less likely not to store household products safely (23% reduction in odds) and not to have taught children rules about what to do if medicines are left on the worktop (34% reduction in odds). Parents of children who had had a poisoning in single adult households were more likely than control parents not to store household products at adult eye level or above (PAF 50%). Parents of girls who had had a poisoning were less likely than parents of controls not to lock medicines away (41% reduction in odds).
Compared with parents of controls, parents of children who had had a scald were more likely to have left hot drinks in reach of children (PAF 31%) and more likely not to have taught children rules about climbing in the kitchen (PAF 20%), about what to do or not to do when adults are using the top of the cooker (PAF 26%) or about hot things in the kitchen (PAF 26%). Parents of children who had had a scald were less likely than control parents to have left a child alone in the bath (53% reduction in odds) and their children climbed or played on furniture less often (38% reduction in odds). Compared with controls, families with at least two adults in paid work whose children had had a scald were more likely not to have taught children rules about what to do or not to do when in the bathtub (PAF 33%). Single adult families with children
who had had a scald were less likely than controls to report an unsafe or unknown hot water temperature (58% reduction in odds). Compared with parents of controls, parents of children with a scald living in rented accommodation were more likely not to check the bathwater temperature with a thermometer (PAF 36%).
Most exposures were study specific. Not using safety gates (other than on stairs) was an exposure in all five case–control studies and ORs were>1 for all studies (ranging from 1.05, 95% CI 0.80 to 1.37 for
poisonings to 1.65, 95% CI 1.29 to 2.12 for falls from furniture). All case–control studies included exposures related to teaching children safety rules, but only teaching rules about climbing in the kitchen was measured in more than one study, with both studies finding ORs>1 (falls from furniture OR 1.58,
95% CI 1.16 to 2.15; scalds OR 1.66, 95% CI 1.12 to 2.47). Across all studies, nine of the 13 ORs related to teaching safety rules were>1 (ranging from 1.13, 95% CI 0.83 to 1.52 for rules about slippery floors
and falls on one level to 1.95, 95% CI 1.33 to 2.85 for rules about what to do or not do when parents are using the top of the cooker and scalds).
Strengths and limitations
We report the largest case–control studies to date examining associations between a range of modifiable risk factors for falls, poisoning and scalds. These studies were conducted in NHS hospitals across England, including urban and rural areas. Adjustment was made for a wide range of potential confounding factors using DAGs. For four of our five studies, the majority of ORs using multiply imputed data for the main analysis did not differ by>10% from those in the complete-case analysis. However, in most studies, a
larger number of ORs in the interaction analyses differed by>10% between the multiple imputation and
the complete-case analyses.
Case–control studies have limitations arising from their observational nature. These include, but are not limited to, measurement error, a range of different types of bias and confounding. Each of these are discussed below. We validated measures for exposures when possible and found high (>70%) sensitivities
and specificities for six out of 12 falls exposures, for two out of 15 poisoning exposures and for two out of three scalds exposures. We used home observations as the‘gold standard’, but it is possible that families may have made changes to their homes either as a result of the injury or in anticipation of the home observation. In addition, there may have been some social desirability bias, with parents reporting responses that they judged to be‘more acceptable’. These may potentially explain some of the lack of agreement that we found between parent-reported and observed exposures. It is likely that some misclassification of exposures occurred. Misclassification is likely to be lowest when sensitivity and specificity are both high. Sensitivity and specificity were both>70% for having safety gates on stairs or across kitchen doorways,
having carpeted stairs and landings part-way up stairs, having playpens, furniture corner covers and cordless or curly-flexed kettles and storing household products at adult eye level or above. For other exposures, when misclassification is higher it is more likely that ORs are biased towards the null (although this does not always occur86) and this may partly explain our failure to find associations between some exposures and falls,
poisonings and scalds. We did explore whether or not the differences between self-reported and observed exposures varied between cases and controls, and we found similar levels of under- and over-reporting for both groups for most exposures. This suggests that differential misclassification is unlikely to have occurred to a large extent. Our analyses did not take misclassification of exposures into account, and for this reason our findings should be interpreted with caution. Future studies should consider adjusting for exposure
misclassification.
The participation rates for cases and controls were similar, but were low for all studies, ranging from 24% to 35% for cases and from 24% to 33% for controls across the five studies. If reasons for participation are associated with the exposure or outcome of interest, selection bias may have occurred. Our participation rates do not show large differences by case/control status, age and sex, but we were not able to assess the
prevalence of exposures in participants and non-participants, and caution should be exercised in interpreting our findings. In addition to social desirability bias discussed above, recall bias may have occurred. These two types of bias could potentially impact on our ORs in different directions. As most injuries were relatively
minor, it is possible that a small number of controls may have had similar injuries to cases and on the same date as the case injury but did not seek medical attention for those injuries. This could lead to misclassification of cases and controls. However, this is likely to apply to only a small number of controls; hence, we would expect this to have at most only a minor impact on our results. If seeking medical attention is associated with exposures of interest, this may lead to overestimation of ORs, but the extent to which this may have introduced bias is difficult to assess.
Most ORs for not teaching children various safety rules were>1 across the five case–control studies and
were significantly raised for rules about climbing in the kitchen for falls from furniture and scalds and for rules about what to do or not do when parents were using the cooker top and about not touching hot things for scalds. It is possible that parents who use safety rules supervise their children differently from parents who do not use rules and, as we were not able to adjust for this, residual confounding may partly explain these findings.
In all five case–control studies, cases were more disadvantaged than controls. Socioeconomic disadvantage is likely to be associated with some of the exposures of interest in our studies and, although we adjusted for a range of confounders, it is possible that some residual confounding remained. It is also possible that families belonging to black and minority ethnic (BME) groups were under-represented in our studies and that for some studies (scalds in particular) a higher proportion of cases than controls belonged to a BME group. The proportion of the population reported as white in the 2011 UK census was 86%,87whereas
the proportion of cases and controls from a BME group ranged from 8% to 18% and from 7% to 9%, respectively, across our five studies. The generalisability of our findings to BME groups may therefore be limited.
Overall, there were few significant interactions found, but our interaction analyses should be interpreted with caution for several reasons. First, a large number of tests for interactions were performed and, although we used a significance level of 1% for these tests, one in every 100 tests will be significant by chance alone. Second, subgroup numbers were small for many comparisons, leading to insufficient power to detect anything other than large differences in associations. Third, differences in estimates of associations between complete-case and multiple imputation analyses suggest that the findings of some of our interaction analyses were not robust to missing data. Consequently, these analyses should be considered as generating rather than testing hypotheses. The significant interactions that were found need confirmation from further research.
Our findings in relation to age are, in general, in keeping with what would be expected based on child development. For example, the increased odds of falls from furniture only in 0- to 12-month-olds who were left on, had nappies changed on or who were put in car/bouncing seats on raised surfaces is to be expected given that these are activities likely to be undertaken by parents whose children are not independently mobile. We found only a small number of exposures with significant interactions with sex, with the exposure more strongly associated with an injury in boys than in girls. The majority of these were in the poisonings case–control study. Boys have higher mortality rates for poisoning than girls88and have
been found to have higher hospital admission rates for poisonings than girls,55,89although some studies
including poisonings not requiring hospital admissions have failed to find significant differences by child sex.90,91As our cases mainly included minor injuries, this would be consistent with finding only a few
exposures more strongly associated with poisonings in boys than in girls.
There were significant interactions for several exposures related to teaching safety rules with either the number of adults in the household or the number in paid work in the stair falls and scalds studies. Previous research suggests that parents start teaching safety rules between the ages of 2 and 4 years and at this point they move from mainly using strategies based on supervision and changing the home environment to teaching- and rule-based strategies to prevent injury.92,93Previous research also suggests that teaching
safety rules can increase the risk of injury93,94and that teaching needs to increase children
’s understanding of the safety issue to reduce the extent to which they interact with hazards.94Our findings suggest that
cases in single adult households and in households without adults in paid work are more likely to have been taught safety rules than controls. It is possible that families in which supervision may be more challenging (e.g. single adult households) or with fewer material resources (e.g. those without adults in paid work) rely more on teaching safety rules than on other injury prevention strategies, but this may not be an effective strategy in these circumstances. Further work is required to explore these hypotheses. The many exposures in our studies resulted in multiple significance testing; hence, some associations may have been significant by chance alone. Our estimates of associations for some exposures were imprecise because of the low prevalence of some exposures such as use of playpens or stationary activity centres, use of safety gates to prevent access to gardens, transferring household products or medicines to other containers or baths being run by older children. Some exposures were not measured in our studies because they were known to be rare, and our studies were underpowered to detect anything other than implausibly large associations. For example, bunk bed falls account for only 10% of falls from beds and have an annual incidence rate of 0.3 per 1000 children-years.45,95–98
Comparisons with existing literature
Comparing our findings with those of previously published studies has been limited by differences in the exposures measured, similar exposures measured in different ways or inadequately detailed descriptions of exposure measures. We have not compared our findings to studies in which cases represent a wide range of injury mechanisms99because of the difficulty in interpreting findings that are not specific to single injury
mechanisms. We found only one Australian case–control study of infants with head or face trauma100
matched on age to controls with which to compare the findings from our falls studies. The findings of the Australian study were consistent with our findings for changing nappies on high surfaces (OR 1.77, 95% CI 1.07 to 2.92) and use of high chairs without harnesses (OR 1.47, 95% CI 0.73 to 2.98). We found slightly raised odds of a fall from furniture for children who had not used a baby walker (OR 1.22, 95% CI 0.90 to 1.65) but slightly reduced odds of a fall on one level (0.83, 95% CI 0.58 to 1.10) and for a fall on stairs or steps (AOR 0.83, 95% CI 0.62 to 1.09), which was consistent with the results from the Australian study (OR for ever using a baby walker 0.83, 95% CI 0.50 to 1.38). However, this was inconsistent with the increased odds of a head injury in those using a baby walker most days (OR 2.47, 95% CI 0.97 to 6.48) found by the same study.
There are several case–control studies that we can compare the findings from our poisonings study with. A study from Greece including children predominantly aged 2–4 years attending hospital emergency clinics following a poisoning and non-injured age-, sex- and hospital-matched controls attending other outpatient clinics found no significant association between mother’s use of safely packaged products, mainly for detergents, and poisoning attendance (OR not presented).101An Australian study of 1- to 3-year-olds
attending an ED following a poisoning and three different types of controls (community, ED attenders with another type of injury and ED non-injured attenders) found that a 1% increase in the percentage of medicinal substances stored in accessible locations in bathrooms increased the odds of poisoning by 3% (OR 1.03, 95% CI 1.002 to 1.080).102
A case–control study from Thailand of children aged<5 years attending hospitals following a poisoning
matched with controls on age, sex and area of residence found no association between toxic substances in the home, storage practices, frequency of use, packaging or disposal practices and poisoning (ORs not presented).103A case
–control study from Brazil of children aged<5 years treated in hospital, matched with