Using the percentage of cases coded as unspecified as an indicator of the quality of cause-of-death reporting for unintentional drowning deaths using ICD-10 codes, our findings indicate that in one in seven of the countries studied the quality of cause-of-death reporting was less than acceptable. Factors associated with the coding of unintentional drowning deaths as unspecified may result from different factors, such as a lack of specific information regarding the circumstances that led to the drowning, the inadequate collection of primary data owing to insufficient police and medico-legal investigation, and incompleteness or errors during the death certification and coding process. In addition, countries may focus on different aspects of drowning for their prevention programmes and therefore require differing levels of specificity in the ICD-10 codes. For example, El Salvador may require more details about the place of occurrence of the drowning at the 4th character code level and place less emphasis on the body of water, whereas in New Zealand the focus may be more on coding information about the body of water involved and less on the place of occurrence. Additionally, the use of a national modification of the ICD-10 in New Zealand may have had an effect on reporting of place of occurrence, as the modification utilizes different codes compared with the international version of the ICD-10.
An international comparison study indicated that the main reason for which injury-related deaths are coded as unspecified is that medical certifiers (including medical examiners and coroners) fail to report sufficiently detailed information on the death certificates to allow coders to assign specific codes [12]. Another study also indicated that despite the legal requirement that all unnatural deaths be subjected to forensic investigation by a physician in Thailand, the cause of death is usually described in terms of symptoms rather than attributed to a specific underlying cause, because physicians are reluctant to provide specifics and risk involvement in legal proceedings [13]. Parish also suggests that a lack of standardised methods and inadequate training for certifiers, medical examiners and coroners in addition to a lack of adequate resources for conducting investigations of deaths results in variations in the quality of mortality data for injury surveillance [14]. More efforts should focus on training medical certifiers to report specific information relevant to injury prevention on death certificates.
The circumstances and environments that result in drowning deaths differ between countries according to the reported ICD codes. The differentiation of mechanisms of drowning deaths into 'while in water' from 'following a fall into water' is one of the important changes in the ICD-10. The two circumstances have different implications for injury prevention. For instance, drowning while in water would mandate the promotion of personal flotation devices and ensuring adequate supervision, whereas drowning following a fall into water would underscore the value of effective barriers. A percentage of drowning deaths coded as unspecified that was high and skewed to one particular mechanism of drowning would bias comparisons of mortality between the two mechanisms. We recommend caution in interpreting the possible effects of unspecified coding on the comparison of international drowning mortality data by sub-category.
One of the limitations of this study was our use of secondary mortality data from the WHO, which lacks metadata about how each country collects information concerning circumstances resulting in and the mechanisms of unintentional drowning as well as the process of death certification and coding. The second limitation was that many countries do not yet use the ICD-10, and some countries had no available population data; having such data available would have contributed to a more complete picture of the global status. The third limitation was the difficulty in defining 'high quality' according to the percentage of cases coded as unspecified; in this study, we used a cut-off of 10%. There is no internationally recognized standard to calculate the quality of coded data. This study is simply an initial assessment of the global status of the provision of specific information in cases of death due to unintentional drowning, and further studies are needed to explore the exact reasons for the high number of cases of unintentional drowning coded as unspecified in various countries.
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