claims data (Noe et al., 2012). Hypothermia resulted in higher mortality rates, longer hos- pital stays, and higher total healthcare costs, however, indicating an increased burden of cold-related illness and death among older adults (Noe et al., 2012). Other studies have found higher rates of cold-related illness and death among men and individuals experienc- ing homelessness. A study from New York City (Lane et al., 2018) found that men, older adults, and those with multiple chronic conditions were more likely to be hospitalized or die due to cold exposure compared with those treated and released from the emergency depart- ment (ED). The most common chronic conditions found among those hospitalized with cold-related illness included cardiovas- cular disease, substance use, and mental ill- ness (Lane et al., 2018). The majority of the state of Minnesota is located in the humid continental climate zone, a zone that is characterized by hot summers and cold winters (Peel et al., 2007). Despite being in a cold weather climate zone, however, cold-related illness and death have not been systematically monitored by the Minnesota Department of Health. The Cold- Related Illness Content Work Group within the CDC Environmental Public Health Track- ing Network piloted the case definition in Kentucky, Massachusetts, New Jersey, New Mexico, New York, Vermont, and Wisconsin, as well as in New York City. The case defi- nition excluded events occurring during the hot season—defined as the months of May through September—due to evidence from the pilot testing suggesting that events in the hot season were related to cold water expo- sure rather than cold temperature. Our assessment evaluated the utility of this case definition for cold-related illness and death in Minnesota. The findings from this assessment can be used to identify vulner- able populations and develop targeted inter- ventions to prevent adverse outcomes from cold exposure in Minnesota and inform other jurisdictions about monitoring cold-related illness and death. Methods Cold-related illness and death in Minnesota were assessed using the International Classi- fication of Diseases (ICD), 9th and 10th Revi- sions, Clinical Modification (ICD-9-CM and
ICD-10-CM) codes from the case definition developed by the Cold-Related Illness Content Work Group. We examined Minnesota Hospi- tal Discharge Data (MNHDD) for ED visits and hospitalizations for cold-related illness from 2000 to 2018, the period for which complete data were available. MNHDD is a comprehen- sive data set that includes patient-level claims data from the majority of hospital visits in the state (excluding the Minnesota Department of Veterans Aairs and Indian Health Service). We defined ED and hospital cases as patients with any ICD-9-CM diagnosis code of 991 (“eects of reduced temperature”); external cause of injury code E901.0, E901.8, E901.9, or E988.3 (“excessive cold” or “extremes of cold” of unintentional or unde- termined intent); or ICD-10-CM code of X31, T68, T69, T33, or T34 (“exposure to exces- sive natural cold,” “hypothermia,” “other eects of reduced temperature,” “superficial frostbite,” or “frostbite with tissue necrosis”) in any diagnosis field. We excluded records with any diagnosis of ICD-9-CM E901.1 or ICD-10-CM W93 (“excessive cold of human- made origin”) and non-Minnesota residents. Cold-related deaths occurring from 2002 to 2019, the period for which complete data were available, were examined using death certificate data provided by the Minnesota Center for Health Statistics at the Minnesota Department of Health. Cases were defined as deaths among Minnesota residents with an ICD-10-CM code of X31, T68, T69, T33, or T34 as an underlying or contributing cause of death. We excluded records with any diag- nosis of ICD-10-CM W93 and intentional deaths. We also excluded any out-of-state deaths, as we included only Minnesota death certificate records from Minnesota residents in our analysis. The case definition for cold-related illness was developed and piloted by the Council of State and Territorial Epidemiologists and the Cold-Related Illness Content Work Group. We explored this case definition by examin- ing the proportion and type of events that occurred outside of the cold season. The cold season was defined as January–April and October–December, and the hot sea- son was defined as May–September. We also explored the hypothesis that cases in the hot season might be related to cold water expo- sure. Water-related ICD-10 codes included W69, W70, and W74 (“accidental drown-
ing and submersion while in natural water,” “drowning and submersion following fall into natural water,” and “unspecified cause of accidental drowning and submersion”). After examining the proportion and type of cases in the summer months, we calculated rates for the cold months using the current winter season case definition. We conducted descriptive statistics for cold-related illness and death in Minnesota. The annual number and rate of cold-related ED visits, hospitalizations, and deaths were calculated by age and sex. Race data were incomplete and homogeneously White. The most recent 5 years of data were aggregated for cold-related ED visits and hospitaliza- tions, while 10-year aggregated data were used for cold-related deaths. We extracted Minnesota population esti- mates for the relevant years from the U.S. Census Bureau and American Community Survey. Age-adjusted rates were calculated using the direct method and the U.S. 2000 standard population. We compared rates of cold-related illness and death across sex and age groups using variance testing (ANOVA) with post hoc Tukey tests. Statistical signifi- cance was defined as p < .05. We also exam- ined the prevalence of cardiovascular dis- ease, respiratory conditions, substance use, mental illness, and diabetes that co-occurred with the cold-related diagnosis, as these conditions are known contributing factors for cold-related illness and death (Berko et al., 2014; Gronlund et al., 2018; Lane et al., 2018; Nixdorf-Miller et al., 2006).
Results
Surveillance Window Approximately 1 in 10 (10%) cold-related ED visits and hospitalizations from 2000 to 2018 occurred during the hot season, while >90% of cold-related ED visits and hospitalizations occurred during the cold season (Table 1). Similarly, only 6% of cold-related deaths from 2002 to 2019 occurred during the hot season, compared with 94% during the cold season. During the hot season, the highest propor- tion of ED visits, hospitalizations, and deaths occurred in May. Overall, the highest propor- tion of cold-related illness and death in any month occurred during January. The type of cold-related illness and death events in the hot season were similar to
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