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Impact of Heat Waves on Mortality --- Rome, Italy, June--August 2003

During June--August 2003, record high temperatures were reported across Europe; Italy was one of the countries most affected. To assess the impact of the summer 2003 heat waves on mortality, the Rome Local Health Authority analyzed temperature and daily mortality data for June--August 2003. This report summarizes the results of that analysis, which indicated that an estimated 1,094 excess deaths occurred during three major heat wave periods in 2003, an increase of 23% compared with the average annual number of deaths during 1995--2002. Improvements have been made in warning systems and prevention programs that target persons at high risk to reduce excess mortality during future heat waves.

Data on daily deaths during June--August 2003 were obtained from the Mortality Registry Office of Rome. Deaths caused by injury and poisoning (International Classification of Deaths, Ninth Revision: 800--999) and deaths that occurred outside Rome were excluded from the analysis. Maximum apparent temperature (MAT)* was defined as an index of human discomfort on the basis of air temperature and dew point temperature (1). A major heat wave period was defined as MAT >90th annual percentile and an increase of 4° F (2° C) compared with the previous day. Daily excess mortality was defined as the difference between the number of deaths observed on a given day and the smoothed average daily value for the reference period (1995--2002). Confidence limits were determined by assuming a Poisson distribution. Association between excess mortality and socioeconomic status was evaluated for the census tract of residence by using a deprivation index based on education, occupation, unemployment, number of family members, overcrowding, and household ownership (2).

During June--August 2003, the mean daily temperature was 5° F (3° C) above the mean for the reference period, and MAT was 95° F (35° C), compared with 88° F (31° C) for the reference period. During June--August 2003, MAT was >91° F (>33° C) (90th annual percentile) on 55 days (72%), compared with 35% of days during the reference period. Three major heat wave periods occurred during June--August 2003. The first episode (June 9--July 2) registered a mean MAT of 97° F (36° C), with peaks of 100° F (38° C) and 104° F (40° C); the second episode (July 10--30) had a mean MAT of 97° F (36° C) and registered two peaks >104° F (>40° C); and the third episode (August 3--13) was shorter but registered a mean MAT of 100° F (38° C), with 3 days >104° F (>40° C).

Daily mortality trends followed temperature trends, with peaks in deaths occurring on the same day as or <2 days from peaks in MAT. During June--August 2003, both temperatures and mortality trends were consistently above the long-term trend, and total mortality was 22.8% higher than expected, with an estimated 1,094 excess deaths (Table). The first heat wave was associated with an increase in mortality of 352, with peaks in mortality of 87 deaths on June 14 (daily excess mortality: 58%) and 88 deaths on June 26 (daily excess mortality: 54%), corresponding to peaks in MAT of 100° F (38° C) and 104° F (40° C), respectively. During the second heat wave, 319 excess deaths occurred; a peak in mortality (89 deaths) occurred on July 25 (daily excess mortality: 68%), with a lag of 1 day. A second peak in mortality (84 deaths) occurred on July 27 (daily excess mortality: 55%), coinciding with the peak MAT (106° F [41° C]). During the third heat wave, 170 excess deaths were reported. Peaks in mortality occurred on August 8 and August 12, with 77 (excess mortality: 48%) and 78 (excess mortality: 59%) daily deaths registered <2 days after peaks in MAT (102° F [39° C] and 106° F [41° C]).

Excess mortality occurred only among persons aged >65 years and increased with age, with the greatest impact on persons aged >85 years (623 deaths; excess mortality: 45.7%) (Table). The greatest increase in mortality occurred among females (estimated daily excess: 35%), reflecting the higher proportion of women aged >85 years (age distribution: women, 72%; men, 28%). A higher excess mortality was observed for out-of-hospital deaths (22.6%) than for in-hospital deaths (6.4%). Excess mortality was associated with socioeconomic status, with an excess mortality of 5.9% among persons in the highest level and 17.8% among those in the lowest level (Table).

Reported by: P Michelozzi, MS, F de' Donato, MS, G Accetta, PhD, F Forastiere, PhD, M D'Ovidio, MS, C Perucci, MD, Dept of Epidemiology, Rome Local Health Authority, Italy. L Kalkstein, PhD, Center for Climatic Research, Univ of Delaware, Newark, New Jersey.

Editorial Note:

During summer 2003, the early onset of hot weather, unusually high temperatures, and prolonged heat-stress conditions caused extreme peaks in mortality throughout Europe. The total number of heat-related deaths that occurred during the summer 2003 heat wave is unknown. However, excess mortality data from five countries (France, Italy, Portugal, Spain, and the United Kingdom) indicate that the potential impact of heat waves on health was underestimated and that health authorities were unprepared to cope with this emergency.

During June--August 2003, record excess mortality occurred in Rome during three intense heat waves. The greatest increase in mortality occurred among persons aged >65 years living in the most economically disadvantaged areas of the city. The high number of excess deaths in this population might reflect the number of elderly persons of low socioeconomic status who remained in the city during the summer. Other socioeconomic factors that might have an impact on health include poor housing quality, absence of air conditioning, lack of access to social and health services, and individual behaviors (e.g., alcohol consumption and taking medication). Although the third heat wave was shorter, it was more intense, with higher temperatures. Lower peaks in mortality observed during the third wave might be attributed to a reduction in the susceptible population, as observed in other cities (3).

Episodes of heat-related mortality in Rome have been reported in previous summers (4). In 1999, Rome was included in a World Meteorological Organization project on cities at high risk for heat-related morbidity and mortality. In 2002, the city implemented a heat health-watch warning system (HHWWS) for the prevention of heat-related deaths during heat waves (9,10) and a public health intervention program targeted at persons at high risk (e.g., persons aged >65 years and those suffering from chronic disease) during extreme weather conditions (5,6). In 2001, of the estimated 2.7 million persons living in Rome, 486,000 (18%) were aged >65 years (National Italian Institute of Statistics, unpublished data, 2001), and the mean annual number of deaths recorded was 26,000 (7,8).

Rome's HHWWS analyzes meteorological forecast data during May--September to predict oppressive air masses and related excess mortality and issues an alarm when these two conditions are forecast. The alarm is upgraded to an emergency when these conditions persist for >2 consecutive days. During summer 2003, the HHWWS called an alarm on 23 days (25%) and an emergency on 20 days (22%). During heat waves, warning bulletins are posted on a municipal website and disseminated to health authorities. Guidelines for the general population and for patients suffering from specific diseases were developed in collaboration with the Association for General Practitioners. The plan is activated on alarm and emergency days to alert public and private subjects (e.g., clinicians, nursing homes, social centers for the elderly, and hospitals) and to provide information to the public (3). A telephone assistance service for elderly persons is available 24 hours a day, 7 days a week. This service provides regular check-in calls, counseling, home delivery of food and medicine, and other services to registered users. A network of social services, volunteers, and street units trained to handle emergencies is activated during the summer months. The Rome Municipality continuously informs elderly persons on the location of social centers and public buildings with air conditioning.

In Italy, as in most of Europe, the increasing proportion of elderly persons and the possible effects of global warming could make the susceptible population more vulnerable to heat waves, leading to increased heat-related mortality. To prepare for possible heat waves in 2004, Rome health authorities have improved the technical capacity of the HHWWS and strengthened municipal prevention programs targeting susceptible populations.

Acknowledgment

The authors acknowledge the assistance of the National Center for Environmental Health, CDC.

References

  1. Kalkstein LS,Valimont KM. An evaluation of summer discomfort in the United States using a relative climatological index. Bulletin of the American Meteorological Society 1986;67:842--8.
  2. Michelozzi P, Perucci CA, Forastiere F, Fusco D, Ancona C, Dell'Orco V. Inequality in health: socioeconomic differentials in mortality in Rome, 1990--95. J Epidemiol Community Health 1999;11:687--93.
  3. Braga AL, Zanobetti A, Schwartz J. The time course of weather-related deaths. Epidemiology 2001;12:662--7.
  4. CDC. Heat-related mortality---Latium region, Italy, summer 1983. MMWR 1984;33:518--21.
  5. Michelozzi P, Fano V, Kirchmayer U, Becker M, Forastiere F, Perucci CA. Public health programmes for the prevention of negative health effects of combined climate and air pollution conditions in the City of Rome. Annual meeting of the Spanish Epidemiology Society, Barcelona, Spain, September 14, 2002.
  6. Fano V, Michelozzi P, Cadum E, et al. Prevention of health effects of heat waves in various Italian cities: the Heat/Health Watch/Warning System. Annual meeting of the International Epidemiology Association, Toledo, Spain, October 1--4, 2003.
  7. National Institute of Statistics. Census 2001: 14th general population and housing census. Available at http://dawinci.istat.it/pl/index_eng.html.
  8. Michelozzi P, Barca A, Capon A, Fano V, Kirchmayer U, Perucci CA. Mortality in Rome and the Lazio region, 1993--98. Rome, Italy: Regional Health Authority, Agency for Public Health, 2000. Available at http://www.asplazio.it/asp_online/stato_salute/Sim_93_98/index.htm.
  9. Kalkstein LS, Nichols MC, Barthel CD, Greene JS. A new spatial synoptic classification: application to air mass analysis. International Journal of Climatology 1996;16:983--1004.
  10. Sheridan SC. The re-development of a weather type classification scheme for North America. International Journal of Climatology 2002;22:51--68.

* Calculated as -2.653 + 0.994Ta + 0.0153 (Td2).  


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