We compared the symptoms, risk factors and possible sources of giardiasis in persons who had travelled abroad before the onset of symptoms to persons who were considered to have domestically acquired giardiasis. Over two thirds of the reported giardiasis cases in Finnish citizens were related to travelling abroad. The travel-related and non travel-related cases did not differ in terms of the severity or duration of symptoms or medication. In non travel-related cases the major risk factors for infection included drinking water from nature, drinking well-water and swimming in a lake. Giardia should be considered as an agent of domestic infection among patients with long-lasting gastrointestinal illness.
Giardia is a highly infectious protozoan parasite capable of causing gastrointestinal illness. During the past decade, the number of Giardia infections reported in Finland has remained stable (approximately 300 cases per year; 4.3-6.5 cases per 100,000 population per year), except in 2008 when the incidence was 8.1 cases per 100,000 population due to a large waterborne outbreak (1). Most of the infections are considered to be of foreign origin among tourists infected abroad. We compared the symptoms, risk factors and possible sources of giardiasis among persons who had travelled abroad before the onset of symptoms to persons who were considered to have a domestically-acquired giardiasis.
Materials and Methods
In Finland (5.3 million inhabitants), clinical laboratories are obliged to notify Giardia findings to the Finnish Infectious Disease Registry (FIDR). A nation-wide, population-based study was conducted during a 15-month period, from 1 June 2005 to 31 August 2006 based on Giardia notifications in the FIDR. The study was approved by the Institutional Review Board of the National Public Health Institute, Finland.
Contact information for persons with Giardia infection was received from the Finnish Population Registry. Data were collected by a self-administered questionnaire sent by mail in May and October 2006 and February 2007. Information was collected on demographic characteristics, underlying illnesses affecting immune defence, symptoms of illness, water exposure and animal contacts. The persons were interviewed regarding exposures during the 30 days preceding onset of illness. If the participant was a child under the age of 16, the parent or the guardian was asked to complete the questionnaire on the behalf of the child.
Case definitions. A travel - related case was a Finnish citizen with a laboratory- confirmed Giardia infection between 1 June 2005 and 31 August 2006 who had been travelling abroad within one month before the onset of symptoms (diarrhoea, abdominal cramps, flatulence or weight loss). A non travel-related case was a Finnish citizen with a laboratory-confirmed Giardia infection between 1 June 2005 and 31 August 2006 who had not been travelling abroad within one month before the onset of symptoms. Persons meeting the case definitions were eligible while persons not reachable by mail or refusing to participate were excluded from the study. Cases that reported duration of illness longer than 2 years were excluded because of recall bias. Cases that were part of an outbreak investigated by public health officials were also excluded.
Data were entered into an electronic database created by Microsoft Access 2003. Analyses were performed by using STATA11 statistical software (Stata Corporation, College Station, TX, USA). Differences in proportions between groups were assessed using the chi-square test. Differences in distributions of continuous variables were assessed using the Kruskal-Wallis equality-of-populations test.
During the study period, no outbreaks of giardiasis were notified by public health authorities. In the surveillance population, 392 persons with Giardia infection were reported. Among the infected persons, 249 (64 %) were Finnish citizens and 181 (73%) responded. In the FIDR notifications, travelling abroad or immigration was mentioned for 58 (32%) persons while for 9 (5%) no travel abroad was reported. Information on travelling abroad was missing in the notifications for 114 (63%) persons.
Fifteen persons were excluded due to absence of symptoms (10 persons) and duration of illness longer than 2 years (5 persons) yielding 166 cases for the final analysis. The non travel-related case definition was met by 45 cases and the travel-related by 121 cases. The travel destinations included Asia (52 cases), Africa (31 cases), South America (18 cases) and European countries and Russia (15 cases).
Table 1. Characteristics of the cases and their symptoms
Males predominated among the non travel-related cases while in travel-related cases the genders were equally presented (Table 1). The travel-related cases were younger than those not related to travelling abroad (p<0.001; Figure 1). No clear seasonality was seen among the cases (Figure 2). The most common symptoms reported by the cases were diarrhoea, flatulence, abdominal cramps and weight-loss (Table 1). The majority of the cases were treated with antibiotics; 86/92 (93%) reported use of metronidazole, 13/92 (14%) tinidazole and 1/95 (1%) albendazole preparations.
Fig. 1. Number of giardiasis cases according to the age group among travel-related and non travel-related cases
Fig. 2. Number of giardiasis cases according to the season of the onset of symptoms among travel-related and non travel-related cases
In univariate analysis, cases that had not been travelling abroad were significantly more likely to have been drinking unboiled natural or well-water, or swimming in a lake in Finland than cases with a travel history (Table 2). In multivariable analysis, the odds ratio of drinking natural water was not possible to estimate due to a low number of observations. When this variable was excluded from the analysis, swimming in a lake (OR 6.8, 95% CI 2.4-19.8, p<0.001) and drinking well-water (OR 5.9, 95% CI 2.5-13.6, p<0.001) remained significant in the model.
Table 2.Univariate analysis of exposure factors for giardiasis among Finnish citizens, 2005-2006
The most common source of infection suspected by the cases themselves was travelling abroad 104/145 (72%). Contaminated water or food (17 cases), adoption from abroad (11 cases) and contact with a possibly infected person (6 cases) were also mentioned. Two cases suspected animal contact with mice and cattle, and one with a ferret that tested positive for Giardia.
Over two thirds of the reported giardiasis cases among Finnish citizens were related to travelling abroad. The majority of the cases had been travelling to far distant destinations, mainly to Asia and Africa. Travelling abroad was also considered the main source of Giardia infection by the cases themselves. In FIDR, travelling abroad was mentioned only in one third of the Giardia notifications indicating that reporting of travel history is not reliable with respect to giardiasis cases.
The travel-related and non travel-related cases did not differ in terms of symptoms, severity or duration of the symptoms or medication. Symptoms reported by the cases were typical for Giardia infection and most frequently included diarrhoea, flatulence, abdominal pain and significant weight-loss. Previously, the duration of relapsing gastrointestinal illness has been reported to be as long as 10 months (2). In this study, most of the cases described an illness that lasted months, and one third of the cases were unable to work or perform household tasks. The length of the illness and the severity of the symptoms cause a significant disease burden. Several cases reported giardiasis-like symptoms that had lasted for years, and some responses reflected a strong frustration with the long duration of illness.
Giardia can be transmitted to a person directly from another person, through the environment and probably from an animal (3). The association of giardiasis with water consumption and swimming is well established (4,5). Among non travel-related cases included in our study the major risk factors for infection included drinking water from nature, drinking well-water and swimming in a lake. Travelling abroad, however, may have reduced the possibility of travel-related cases to get exposed in Finland leading to an increase in the frequency among the non travel-related cases. Giardia is known to circulate in Finland’s environment (6, 7) and previously swimming in water from natural sources and drinking water from private supplies has also been proven to be a risk factor for campylobacteriosis in Finland (8). In the present study, the non travel-related cases were older and more often males than the travel-related cases. By nature, the older Finnish males are probably likely to lead a wild life in the wild nature. Apart from travelling abroad and via adopted children, the cases themselves suspected water or food, and contact to other allegedly infected persons (tourists, foreign kitchen staff and foreign partners) as the source of their infection.
Cases enrolled in this study are not representative for all persons with Giardia infection in Finland. Screening for Giardia is commonly included as part of the immigration examination (9). Due to the focus on exposures in Finland, a large number of unknown mailing addresses for non-Finnish citizens and language limitations, only Finnish citizens were included in this study. Furthermore, persons with more severe symptoms, underlying chronic illness and specific age-groups are probably more likely to seek medical care and therefore more likely to be sampled.
During the past decades, giardiasis has mainly been regarded as a traveller’s disease in Finland which might have influenced the decision to test for Giardia in gastrointestinal illnesses (10). Our study demonstrated that one third of Finnish citizens with Giardia infection had not travelled abroad within one month before the onset of symptoms, and that giardiasis in non travel-related cases was associated with water-related exposure factors. Thus, Giardia should also be considered an agent of domestic infection among patients with long-lasting gastrointestinal illness.
Ruska Rimhanen-Finne was funded by grants from the Finnish Veterinary Foundation and the Research Foundation of Orion Corporation.
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