General findings

In 2005, there were an estimated 12,700 hospitalizations that were caused by excessive exposure to heat or cold due to weather conditions. About 6,200 hospitalizations were heat-related stays and an estimated 6,500 hospitalizations were cold-related stays with a combined national hospital cost of over $120 million. The average cost of stays related to cold exposure was more than twice that of those related to heat exposure: $12,500 per cold-related stay compared to $6,200 per heat-related stay. The average cost of all other hospital stays was about $8,100 per stay. The main driver of the increased cost associated with cold-related stays appeared to be the length of time the patient remained in the hospital. The average length of stay for cold-related hospitalizations was 6.7 days which was more than twice as long as the average length of heat-related stays (3.2.days). When the patient’s time in the hospital was accounted for, the cost per day was identical for heat and cold related stays at $1,900 which was comparable to the per day cost of all other hospital stays.

Table 1

Overview of hospital stays resulting from exposure to excessive heat and cold due to weather conditions, 2005.

Patients hospitalized for heat-and cold-related stays were older than the average hospital patient (age 47 years): those hospitalized for excessive heat exposure averaged about 54 years, while those hospitalized for cold-related stays averaged about 59 years. The majority of these hospitalizations began in the emergency department (ED) and subsequently resulted in admission to the hospital (81.6 percent for the heat-related stays and 77.6 percent for the cold-related stays)—a much higher percentage than the 42.5 percent of hospitalizations that began in the ED for all other stays. The percentage of patients who died at the hospital for heat-related stays was 2.9 percent (about 180 patients) which was close to the estimated 2.1 percent of in-hospital deaths among non-related stays. In contrast, the percentage of people who died at the hospital for cold-related exposure was significantly higher at 10.5 percent (about 685 patients).

Rates of hospital stays resulting from excessive heat and cold, by gender, age, and region

Hospitalization rates resulting from excessive exposure to heat and cold due to weather conditions were low compared to all other hospital stays, but still reveal important patterns. Hospitalization rates for both heat- and cold-related stays increased significantly with age and were higher in males. Rates of heat- and cold-related hospitalizations were about 15 times greater in the oldest age group (65+) compared to the youngest age group, 0–17 year olds (about .5 per 100,000 population compared to 6.0 to 7.6 per 100,000 population). Among men, the hospitalization rate for heat-related stays was about 3 times greater than the rate for women and about 1.4 times greater for cold-related stays compared to women.

Regional patterns of hospitalizations due to excessive heat and cold were consistent with the expected climate in each region. Heat-related stays were far more common in the South than in any of the other region (3.1 stays related to heat per 100,000 population in the South compared to 1.4 to 1.7 stays in the remaining regions). In contrast, cold-related stays were much more frequent in the Northeast compared to the other regions (3.7 stays per 100,000 population in the Northeast compared to 1.6 to 2.2 stays in the other regions).

Hospital stays resulting from excessive heat and cold, by median community income

The rate of hospital stays resulting from excessive exposure to heat and cold due to weather was inversely related to wealth: as community-level income increased, the rate of hospitalizations decreased (figure 1). This pattern was seen in all hospital stays as well. In the poorest communities hospitalizations resulting from exposure to heat and cold were about 2 to 2.5 times more common than in the wealthiest communities. Hospitalization rates for heat-related and cold-related stays were similar within each income level.

Figure 1

Rate of hospital stays resulting from exposure to excessive heat or cold due to weather conditions were more common in poor communities, 2005*. *Based on all-listed ICD-9-CM external cause of injury codes (E codes). Note: The denominator for the rates (more...)

Figure 2

Disproportionately more hospital stays caused by excessive heat or cold exposure due to weather conditions were uninsured compared to all hospital stays, 2005*. *Based on all-listed ICD-9-CM external cause of injury codes (E codes). Source: AHRQ, Center (more...)

Hospital stays related to excessive heat and cold, by payer

Government payers, Medicare and Medicaid, were billed for the majority of hospital stays related to excessive exposure to heat or cold due to weather conditions. Collectively, these two payers were responsible for about half of heat-related and nearly 70 percent of cold-related stays compared to about 57 percent of all hospital stays. Relative to its share of all hospital stays (37.2 percent), Medicare—the insurance program for the elderly and disabled—was disproportionately billed for nearly half of stays related to excessive cold, but a comparable portion of heat-related stays (37.6 percent). In contrast, Medicaid—the insurance program for low-income individuals—was billed for about 20 percent of all hospital stays which was similar to its share of cold-related stays (20.4 percent), but was billed for disproportionately less heat-related stays (9.8 percent).

For both heat-related and cold-related hospitalizations, private insurance was billed for significantly less stays compared to its share of all hospital stays (27.4 percent and 14.9 percent of heat-and cold-related stays, respectively, compared to 34.9 percent of all hospital stays). While about 5.6 percent of all hospital stays were uninsured, a much larger portion of stays related to excessive temperatures were uninsured: 16.9 percent of heat-related and 12.8 percent of cold-related stays.

Hospital stays related to excessive heat and cold, by patient location

Hospital stays related to excessive heat and cold were more common in non-metropolitan locations (i.e., rural areas) compared to metropolitan and micropolitan areas (figure 3). While there were less than 2 stays per 100,000 population in large metropolitan areas, in rural areas there were about 3 to 4 stays per 100,000 population for cold-and heat-related stays, respectively. More patients may be hospitalized in rural areas because of relatively poorer access to outpatient health care services compared to those patients residing in metropolitan locations. This pattern was similar to that seen in all hospital stays for which the overall rate of hospital admissions in rural areas was greater than in metropolitan locations.

Figure 3

Rate of hospital stays caused by exposure to excessive heat or cold due to weather conditions were greater in rural areas compared to metropolitan areas, 2005*. *Based on all-listed ICD-9-CM external cause of injury codes (E codes). Source: AHRQ, Center (more...)

Most common reasons for being admitted to the hospital related to excessive exposure to heat and cold due to weather conditions

Patients hospitalized for excessive heat or cold exposure present to the hospital for a specific condition (identified by the principal diagnosis code) with notation in their hospital discharge record that the hospitalization was a result of a weather-related event. More than half of patients hospitalized for exposure to excessive heat were admitted for heat exhaustion and heat/sun strokes. Other reasons for heat-related hospitalizations included fluid and electrolyte disorders (7.6 percent of stays), renal failure (6.4 percent of stays), fainting (3.4 percent of stays) and atherosclerosis (2.1 percent of stays).

Table 2

Top 5 most common reasons for hospital stays related to excessive heat exposure due to weather conditions, 2005.

Among patients hospitalized for cold-related stays, about a third of patients were hospitalized principally for hypothermia and frostbite. Other reasons for hospitalizations included septicemia (6.8 percent of stays), complicated diabetes (6.4 percent of stays), pneumonia (2.7 percent of stays), and fluid and electrolyte disorders (2.6 percent of stays).

Table 3

Top 5 most common reasons for hospital stays related to excessive cold exposure due to weather conditions, 2005.

Diagnoses, Procedures, ICD-9-CM, and Clinical Classifications Software (CCS)

The principal diagnosis is that condition established after study to be chiefly responsible for the patient’s admission to the hospital. All-listed procedures include all procedures performed during the hospital stay.

ICD-9-CM is the International Classification of Diseases, Ninth Revision, Clinical Modification, which assigns numeric codes to diagnoses. There are about 12,000 ICD-9-CM diagnosis codes.

CCS categorizes ICD-9-CM diagnoses and procedures into clinically meaningful categories.² This “clinical grouper” makes it easier to quickly understand patterns of diagnoses and procedures.

Case Definition

External cause of injury codes (E codes) were used to identify heat- and cold weather-related stays. E codes are a type of ICD-9-CM diagnosis code that explain the reasons for hospitalizations.

Types of hospitals included in HCUP

HCUP is based on data from community hospitals, defined as short-term, non-Federal, general and other hospitals, excluding hospital units of other institutions (e.g., prisons). HCUP data include OB-GYN, ENT, orthopedic, cancer, pediatric, public, and academic medical hospitals. They exclude long-term care, rehabilitation, psychiatric, and alcoholism and chemical dependency hospitals, but these types of discharges are included if they are from community hospitals.

Unit of analysis

The unit of analysis is the hospital discharge (i.e., the hospital stay), not a person or patient. This means that a person who is admitted to the hospital multiple times in one year will be counted each time as a separate “discharge” from the hospital.

Costs and charges

Total hospital charges were converted to costs using HCUP Cost-to-Charge Ratios based on hospital accounting reports from the Centers for Medicare and Medicaid Services (CMS).³ Costs will tend to reflect the actual costs of production, while charges represent what the hospital billed for the case. For each hospital, a hospital-wide cost-to-charge ratio is used because detailed charges are not available across all HCUP States. Hospital charges reflect the amount the hospital charged for the entire hospital stay and does not include professional (physician) fees. For the purposes of this Statistical Brief, costs are reported to the nearest hundreds.

Payer

Payer is the expected primary payer for the hospital stay. To make coding uniform across all HCUP data sources, payer combines detailed categories into more general groups:

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Medicare includes fee-for-service and managed care Medicare patients.

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Medicaid includes fee-for-service and managed care Medicaid patients. Patients covered by the State Children’s Health Insurance Program (SCHIP) may be included here. Because most state data do not identify SCHIP patients specifically, it is not possible to present this information separately.

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Private insurance includes Blue Cross, commercial carriers, and private HMOs and PPOs.

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Other includes Worker’s Compensation, TRICARE/CHAMPUS, CHAMPVA, Title V, and other government programs.

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Uninsured includes an insurance status of “self-pay” and “no charge.”

When more than one payer is listed for a hospital discharge, the first-listed payer is used.

Admission source

Admission source indicates where the patient was located prior to admission to the hospital. Emergency admission indicates the patient was admitted to the hospital through the emergency department.

Median community-level income

Median community-level income is the median household income of the patient’s ZIP Code of residence. The income value is missing for homeless and foreign patients.