Between 1 July and 11 August, 109 cases of tularaemia (
Francisella
tularensis var holarctica) were notified to the Swedish Institute of
Infectious Diseases (Smittskyddsinstitutet, SMI) (Figure 1). Sixty per cent
of cases are in men and most of the cases have occurred in people of active
working age (Table 1). Typically, most cases are clustered tightly by geography.
The locations and the total number of cases vary markedly from year to year
(Figure 2).
Table 1. Age and sex distribution of notified tularaemia
cases in Sweden between 1 July to 8 August 2003
| Age |
Female |
Male |
Total |
| 0-9 years |
1 |
9 |
10 |
| 10-19 years |
2 |
6 |
8 |
| 20-29 years |
3 |
3 |
6 |
| 30-39 years |
6 |
8 |
14 |
| 40-49 years |
7 |
16 |
23 |
| 50-59 years |
13 |
11 |
24 |
| 60-69 years |
9 |
10 |
19 |
| 70+ years |
3 |
2 |
5 |
| Total |
44 |
65 |
109 |
Figure 1. Number of notified tularaemia cases by week
of notification, Sweden, 1 July to 11 August 2003. *Only one day (11 August)
of week included. Source: SMI.
Figure 2. Number of tularaemia notifications by year,
Sweden, 1997 - 2002.
The ulcero-glandular form of the disease dominates, with most cases reporting
a mosquito or tick bite at the site of the ulcer and subsequent lymphadenopathy.
This is consistent with the presentation during previous years in Sweden
(1). This year, a few clusters with respiratory disease probably due to
inhalational exposure have also been reported. These cases are typically
in farmers, with onset of disease within a few days of working with hay.
Similar inhalational exposure of farmers has been reported from previous
outbreaks in Sweden and Finland (2,3). Depending on the route of exposure,
tularaemia may also present in the oculoglandular and oropharyngeal forms
(4).
In addition, F. tularensis has also been diagnosed in post mortem
analyses of three hares from one of the affected counties by the National
Veterinary Institute (Statens Veterinärmedicinska Anstalt, SVA) (5).
Reports of dead hares, voles, and other small rodents around the areas with
human cases have been included in many case notifications. The reservoir
of F. tularensis in nature is unknown, although its survival in
water and mud together with the apparent distribution along lakes and rivers
in Sweden and eastern Europe is suggestive of a water associated reservoir
(4).
Mosquito bites, owning a cat, farming, and visiting wooded areas were identified
as independent risk factors for tularaemia in a recent Swedish case-control
study (1). In this study, 16% of the cases were admitted to hospital. Tularaemia
is responsive to antibiotic treatment, if begun within one week of onset
of disease. With adequate treatment, mortality due to infection with F.
tularensis var holarctica is very low. No deaths due to tularaemia
in Sweden have been reported to SMI during this season.
The early start of tularaemia notifications together with the rapid increase
in number of notifications during the first weeks suggest an epidemic year
in Sweden. Despite the proximity of some of the affected areas to the Norwegian
border, no cases had been notified in Norway by 11 August (6). In Finland,
dozens of cases have been reported from the areas affected
during the 2000 epidemic (7).
Tularaemia continues to warrant vigilance during late summer and early
autumn in the Nordic countries. Early identification of case clusters is
useful for correct clinical management of cases. Research is needed to identify
the natural reservoir and other environmental factors contributing to annual
changes in incidence. Natural early warning signals might even allow preventive
measures in affected geographical areas.