Leptospirosis mortality in Cuba:
1987 - 1993.
Oslando Padilla Pérez, B.S. M.D. , C. Herio de Jesús Toledo Vila, M.D., Ignacio Vidal García, B.S.1 , and Iraida Rodríguez, M.D.
Abstract:
A descriptive study of the data available at the National Statistics Division of the Ministry of Public Health on the 397 deaths caused by leptospirosis in Cuba from 1987 to 1993 was conducted. Data were tabulated for age, sex, place of residence, date of death, autopsy findings, and occupation at the time of death. Years of potential life lost were calculated for the 0-65 age group. In 1993, a sharp rise in mortality was observed, peaking at a rate of 1.03 per 100,000 inhabitants. The highest rates were registered among those over 50 years of age, with higher rates in males as a determining factor in overall mortality rates. Incidence was highest in the months of October, November and June. The Isle of Youth Special Municipality and Las Tunas Province registered the highest rates. Retired workers were the most affected, followed by factory and agricultural workers.Subject headings: LEPTOSPIROSIS/mortality; MORTALITY RATE; EPIDEMIOLOGY, DESCRIPTIVE; CUBA.
Leptospirosis is a zoonosis with a worldwide distribution, especially in tropical climates and humid zones. It is caused by spirochetes of the Leptospira genus, which penetrate through the skin and mucous membranes as a result of contact with water polluted by urine from infected animals, most notably rats, mice, cattle, pigs and dogs. The highest occupational risk groups include those who work in rice fields and sugar cane fields, along with other agricultural workers; those working in slaughterhouses or sewerage systems; and those who, as a consequence of their occupational or domestic activities, have direct or indirect contact with the urine of the above-mentioned animals.2
In Cuba, leptospirosis is distributed throughout the country. The number of diagnosed cases had been declining every year until 1987, when a sudden increase was detected. Morbidity rates reached 5.3, 7.2, and 9.8 ´ 100 000 inhabitants in 1992, 1993, and 1994, respectively.3 The most affected provinces were Villa Clara, Ciego de Ávila, Camagüey, and Cienfuegos, and the months in which the most cases were reported were October, November, and December (Han Kala, AL. Leptospirosis humana [Tesis de terminación de residencia de Microbiología] Instituto de Medicina Tropical Pedro Kourí 1992:11-17).
The mortality rate produced by this disease is low but it increases with age and it can reach 20% or more in patients affected by jaundice and renal lesions who have not received dialysis.4-7
In Cuba, leptospirosis mortality increased from 46 in 1990 to 112 in 1993, leading to the decision to undertake this study covering the years 1987 to 1993. Our objectives have been to both trace the increased mortality and to identify the variables distinguishing the population groups where the greatest number of deaths have occurred in order to develop an effective surveillance system.
Methods
Data was obtained from the National Statistics Division of the Ministry of Public Health (MINSAP) on the 397 deaths caused by leptospirosis in Cuba from 1987 to 1993.
The following information was selected for each subject: age, sex, occupation, permanent home address, date of death and autopsy findings.
Population data structured by age, sex, and province was obtained from the Demography Department of the Statistical Research Institute (INSIE) of the National Statistics Committee (CEE).
Data was processed with EPI-INFO, version 6.0, and graphics with the HG3 system. The annual percentage rates and the standardized mortality ratio (SMR) were calculated to express the proportion between the real and the expected rate for every province by age groups. The year 1991 was selected as the standard population for analyzing the mortality rate by age and sex.
Age groups are those typically used by the Ministry of Public Health: less than 1 year; 1-4 years; 5-14 years; 15-49 years; 50-64 years; and over 65.
Occupational analyses were also performed. Percentages, rates per 100,000 inhabitants and years of potential life lost (YPLL) for the 0-65 age group were calculated. Tests for statistical significance were applied (ratio comparisons) to determine differences according to province, sex, and age groups. The Kruskal-Wallis Test was used to determine significance of the monthly variation of mortality by leptospirosis within the period studied.
Results
In this study, the number of annual deaths showed a tendency to rise, from 17 in 1987 to 112 in 1993. Thus, the mortality rate by leptospirosis in Cuba (per 100,000 inhabitants) in the period studied increased from 0.16 in 1987 to 0.42 in 1988, then stabilized until 1990, increased somewhat during 1991 and 1992, and then increased sharply in 1993, reaching a rate of 1.03 (Figure 1).
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A total of 6,238 years of potential life were lost (YPLL) due to the above-mentioned increase in the death rate, which represented 2% of all YPLL for infectious diseases in the country within this period. The most affected year was 1993 with 5.25% (Fig. 2).
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Mean years of life lost was 15, suggesting mortality occurred mainly during adulthood.
With regards to age, three statistically well-differentiated groups were identified: under 15 years of age, with practically zero mortality; 15-49 years, with a mean mortality rate of 0.4077; and over 50 years, with even greater rates (a=0.05) (Table 1). In the 15-49 age group, an increase in the death rate is observed from 1987 to 1988; and again from 1992 to 1993. In the 50-64 age group, the ascending tendency observed from 1987 to 1988 was progressively maintained until 1993. In the over-65 group, the rate was stable until 1990; and a moderate increase was registered from 1990 to 1993, with 2.714 as a final rate for that period, five times more than the 1987 rate which was 0.522.
Table 1. Deaths and rates per 100,000 inhabitants by leptospirosis by year and age group
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There was greater mortality among men in the over-15 group (a=0.01), which was a determining factor in the global rate (Figure 3).
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The greatest numbers of deaths occurred in October; November; and June, in decreasing order.
The Isle of Youth Special Municipality and Las Tunas Province were the two regions of the country demonstrating the highest SMR during the analyzed period, followed by Sancti Spiritus and La Habana Provinces (Figure 4).
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The population group most affected was retired persons (91 deaths during the seven years studied), followed by factory workers (82 deaths) and agriculture workers (62 deaths). (See Table 2).
T able 2. Deaths by leptospirosis by year and occupation.
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Source: National Statistics Division of the Ministry of Public Health.
The percentage of autopsies performed progressively decreased from 94.2% in 1987 to 78.6% in 1993, while the percentage of deaths confirmed by autopsy increased, reaching more than 40% in 1993. (Figure 5).
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Discussion
According to reports received from the Cuban Ministry of Public Health, from 15 to 26 deaths per year were caused by leptospirosis between 1982 and 1986, for an annual mortality rate of 0.2-0.3 (per 100,000 inhabitants).8-14 In the period covered by this study (1987-93), the annual mortality rate was consistently higher than the figures recorded for the previous period, with a sudden increase beginning at the end of the latter.
Similar to other reports in the literature, we found higher mortality during the rainy season.2 In addition, the higher mortality registered among adult men reflects what it is known about risk groups for this disease.
The increase observed in the number of deaths associated with an increased number of cases, though apparently logical, should not have occurred taking into consideration the fact that leptospirosis deaths are eminently preventable with early diagnosis and treatment.
There are at least 3 interesting results deserving further study. First, the provinces most affected between 1982 and 1991 (Villa Clara, Ciego de Ávila, Camagüey and Cienfuegos) had the lowest SMRs at the time of this study, while those provinces with high SMRs during the study did not seem as problematic during the previous period. Thus, a change in the geographical pattern of leptospirosis mortality in Cuba has occurred. Second, in spite of the fact that occupational classifications were derived from the death certificates, which prevented us from applying a more sophisticated analysis, the fact that the "retired" occupational group presented the highest number of deaths is interesting and suggests the possibility that these subjects were retired agricultural and/or domestic workers with greater likelihood of exposure to leptospirosis. Research concerning occupational risk factors for leptospirosis would necessarily require more in-depth information than that available from the death certificate. Third, the fact that this study demonstrates higher death rates among men older than 50 years of age, during June, October and November, 1993, suggests the hypothesis that increased risk and/or diagnostic and treatment delays are significant factors in mortality and require further research.
Finally, we would call attention to the fact that a significantly high percentage of the autopsies in this study reported results as still pending, introducing an unfortunate and unnecessary bias in the research.
References
Leptospiral infection: a household serosurvey in urban and rural communities in Barbados and Trinidad. Am J Trop Med Parasitol 1990; 84(3):255-66.
This article originally appeared in Spanish in the Revista Cubana de Medicina Tropical, vol. 50, No. 1, (pp. 61-65), 1998.
Copyright (c) 1999, MEDICC - Medical Education Cooperation with Cuba