Human Leptospirosis Trends, the Netherlands, 1925–2008

Marga G.A. Goris

, Kimberly R. Boer, Tamara A.T.E. Duarte, Suzanne J. Kliffen, and Rudy A. Hartskeerl

Author affiliations: Author affiliation: Royal Tropical Institute (KIT), Amsterdam, the Netherlands

Abstract

To increase knowledge of leptospirosis in the Netherlands and identify changing trends of this disease over time, we analyzed historical passive surveillance reports for an 84-year period (1925–2008). We found that 2,553 mainly severe leptospirosis cases were diagnosed (average annual incidence rate 0.25 cases/100,000 population). The overall case-fatality rate for patients with reported leptospirosis was 6.5% but decreased over the period, probably because of improved treatment. Ninety percent of reported leptospirosis cases were in male patients. Most autochthonous leptospirosis infections were associated with recreational exposures, but 15.5% of the cases were attributed to accidents that resulted in injury and to concomitant water contact. Since the end of the 1950s, the proportion of imported infections gradually increased, reaching 53.1% of the total during 2005–2008. Most (80.1%) imported infections were associated with sporting and adventurous vacation activities.

Leptospirosis is a zoonotic disease caused by infection with Leptospira spp. bacteria (1). Pathogenic leptospires live in the kidneys of many mammalian hosts, including rodents, insectivores, and livestock. Leptospires are shed into the environment, where they can survive for several months in favorable (warm and wet) conditions. Thus, leptospirosis is particularly endemic to warm and humid tropical and subtropical regions (2). Humans are infected by direct contact with infected animals or indirectly by contact with a contaminated environment.
Leptospirosis is an emerging public health problem globally (3–6). However, this disease is often overlooked because it is difficult to clinically diagnose and because and laboratory-based diagnosis is cumbersome. Because mild leptospirosis frequently goes unrecognized and notification systems are mostly absent, the global incidence of leptospirosis is underestimated. An international survey conducted by the International Leptospirosis Society reported ≥350,000 cases of severe leptospirosis annually (7). This estimate is supported by data from an assessment of the global incidence of leptospirosis (8), which indicated a mean global incidence rate for leptospirosis of 5 cases/100,000 population.
In Europe, leptospirosis has been studied and diagnosed since the 1920s. Historical reviews from Germany (9) and France (10) have contributed to a better understanding of the epidemiology of leptospirosis. In the Netherlands, passive surveillance of human leptospirosis began in 1924. Reporting of cases of this disease is mandatory, and laboratory diagnosis has been centralized in 1 institution. To increase knowledge of leptospirosis, we analyzed historical passive surveillance reports in the Netherlands for 84 years (1925–2008) to determine changing trends of this disease over time.

Passive Surveillance

The Royal Tropical Institute (KIT) in Amsterdam is associated with the World Health Organization/Food and Agricultural Organization/World Organisation for Animal Health and the National Collaborating Centre for Reference and Research on Leptospirosis (NRL), which confirms ≈99% of the suspected cases of leptospirosis in the Netherlands. Detailed records on serologic, clinical, and epidemiologic features are archived at the NRL. Since 1928, leptospirosis has been a mandatory reportable disease in the Netherlands (11). A case of leptospirosis is defined as laboratory confirmation of infection as described in this report and by Hartskeerl (12) and fever or 2 of the following signs and symptoms: shivering, headache, muscle pain, conjunctival injection, bleeding in skin and mucosa, rash, jaundice, myocarditis, meningitis, renal failure, pulmonary hemorrhage with respiratory failure.