Donatella Mandolini, Marta Ciofi degli Atti, Biagio Pedalino*, Antonino Bella, Barbara De Mei, Silvana Parrocini, e Stefania Salmaso
Infectious Disease Unit Laboratory of Epidemiology and Biostatistics *EPIET fellow, CDSC, Belfast, Ireland.
Tetanus is an actute infectious disease, the symptoms of which are caused by an exotoxin produced during the multiplication of Clostridium tetani, an organism that is widely distributed in the soil, in dust, and in the feces of herbivorous animals. The symptoms consist of painful muscular contractions. There are a variety of clinical forms, including localized involvement, generalized disease, and neonatal tetanus. Diagnosis is based on clinical findings, and case-fatality rates are high.
A vaccine that produces a three-dose efficacy in excess of 90% has been available since the 1930s, and as a result of its widespread use, tetanus has become a rare disease in the industrialized world. In Italy, tetanus vaccination was made mandatory for military recruits in 1938. In 1963, recommendations were extended to include children during the second year of life and selected occupational groups considered to be at elevated risk (e.g., those working in agriculture and animal husbandry). In 1967, the recommended age of childhood vaccination was lowered; the current vaccine schedule calls for the three doses to be administered at 3, 5, and 11-12 months of age, followed by booster doses at ages 5-6 years, at 11-15 years, and every 10 years thereafter. At national level, childhood vaccination coverage within the first two years of life is high (95% for the 1996 birth cohort). Nonetheless, there is little information available on the administration of the vaccine in adults, nor on tetanus vaccine coverage in adults and the elderly.
Tetanus reporting has been mandatory in Italy since 1995. It is considered a Class I condition, that requires notification within 12 hours of a suspected case. The surveillance case definition is strictly clinical. As for all vaccine-preventable diseases, surveillance for tetanus is considered essential for the evaluation of the success of vaccination program efforts.
The results reported in this study concern tetanus morbidity and mortality data for 1955-2000. The analysis was performed using data from a variety of sources. To estimate the incidence of the disease, the following sources were used: 1) the historical records of the Italian National Institute of Statistics (ISTAT), which contain annual incidence by age; 2) the individual ISTAT case notifications for 1971-1996 that include date of reporting, date and site of first symptoms, age, and sex; 3) annual notifications aggregated by region, age, and sex provided by the Ministry of Health for 1997-1999; and 4) the Epi-Info data base managed by the Istituto Superiore di Sanità since 1998. In this latter data base, individual case notifications from the local health units throughout the county contain the usual information contained on the reporting form and results of any case investigation performed, including vaccination status.
Information on deaths was obtained from ISTAT’s cause of death records that were available for 1970-1997. This source was used to obtain data on tetanus deaths by year and age. Case-fatality rates were calculated as the ratio between the number of deaths and number of cases notified.
The figure illustrates the number of annual cases from 1955 to 2000. From the mid 1950s to the mid 1960s, a mean of 722 cases were reported annually (1.4/100,000 inhabitants). Subsequently, a rapid decline occurred that lasted until the mid 1970s and which coincided with the introduction of obligatory vaccination for children and various categories of high-risk workers in the early 1960s. Subsequent declines have been slower, with a historic low of 65 cases reported in 1991. From 1992 to 2000, the number of cases has remained stable, with a mean of 102 cases/year (0.2 caes/100,000). The last case of neonatal tetanus occurred in 1982.
With respect to geographic distribution, between 1970 and 1990, the decline in cases was uniform across the country. Indeed, the age-standardized incidence rate per 100,000 residents (reference population: ISTAT census data 1991) declined over the 20 year period from 0.64 to 0.19 in the north, from 0.62 to 0.25 in the center, and from 0.37 to 0.11 in the south. For all periods considered, the rates of tetanus in the south were lower than the national average.
The reduction in the observed incidence between the 1970s and 1990s was apparent in all age groups, as is shown in the table, which reports the distribution by age and sex for three decades. During the entire time period, the highest rate has consistently been in those 65 years of age and over. The greatest decline in incidence occurred in those 15-24 years, where the incidence declined 20-fold. By contrast, the incidence in those >65 years only decreased by half. As a result, the percentage of cases >65 years of age increased from 40% of the total cases in the 1970s to 70% in the 1990s. This phenomenon is also borne out in the data on the median age of cases, which has increased from 58 years in the 1970s to 63 years in the 1980s and 71 years in the 1990s.
In the 1990s, males and females under the age of 65 years had similar incidence rates, while in those >65 years, rates were higher in women. This finding is attributable to the fact that in this age group, women probably have a lower vaccine coverage than their male counterparts who were vaccinated as military recruits or because of job-related risks.
Among the 292 cases reported to the Istituto Superiore di Sanità in 1998-2000, 181 (62%) had information available on vaccination status (56% of men and 65% women). Among those for whom vaccine status was known, 16.4% of the male and 7.1% of the female cases had been vaccinated.
The decline in tetanus cases has been paralleled by a decline in case-fatality, from 64% in the 1970s to 40% in the 1990s.
The current situation reflects vaccine policy over the years. The introduction of vaccine for all infants has led to an 86% reduction between the mid 1950s and the present, and today in Italy tetanus affects those who are unvaccinated or inadequately vaccinated. The decrease in case-fatality is presumably attributable not only to an improvement in health services but also the increase in vaccine coverage since those who have been vaccinated tend to have a milder clinical course.
Unlike diseases which are transmitted person-to-person, a high vaccine coverage in the paediatric age group does not provide indirect protection for the entire population (herd immunity). Furthermore, the ubiquitous presence of tetanus spores in the environment make it practically impossible to eliminate the disease. As a result, all those who are inadequately vaccinated are potentially at risk.
Despite the increase in vaccine coverage and decreases in case rates attained in the 1990s, the incidence of tetanus remains approximately 10 verdana higher than rates in other European countries and the United States (1,2). The fact that those 365 years represent 70% of the cases clearly underlines the need to develop interventions targeted at this age group. In addition to improving post-exposure prophylaxis for the entire population, the administration of tetanus vaccine to the elderly should be considered within the context of the annual influenza vaccination campaigns.
1. Bardenheier B. et al, Tetanus surveillance – United States, 1995 – 1997 MMWR 1998; 47 (SS-2): 1-13.
2. World Health Organization (WHO) Regional Office for Europe. Health For All Statistical Database. Copenhagen December 1999 version. http://www.who.dk/country/country.htm).