Three Trichinella-free Bacons:
Outbreak in Latvia Linked to Bacon Bought at a Market
Between January and March 2005, 45 trichinellosis cases were notified to the Public Health Agency (PHA) of Latvia. This represents a 246 per cent increase compared with the same period in 2004, and involved 42 patients in 3 outbreaks and 3 sporadic cases.
The largest of these outbreaks affected 27 patients and occurred between 28 Feb and 14 Mar 2005. Cases occurred in 3 administrative areas - Riga, the capital of Latvia, the district around Riga, and the Madona district.
Epidemiological analysis linked the infection to eating salted streaky bacon bought at Riga central market. Of the 27 patients, 18 were female and 9 were male (average age 41; range: 13-60). The main symptoms were weakness, nausea, facial edema (in more than half of the cases), and fever. In more than in half of the cases, the body temperature exceeded 38 C. All of the patients were admitted to hospital. The incubation period ranged between 2 and 4 weeks.
The Latvian Food and Veterinary Service (FVS) collected 37 meat samples from retail outlets identified in the investigation, and all tested negative for trichinella larvae. One retail outlet was found to be selling pork of unknown origin which came with falsified delivery notes, so the pork had not been tested for Trichinella spiralis in government-supervised inspections. The descriptive epidemiology of those who were ill strongly implicated this streaky bacon as the vehicle for infection. A case control study was not carried out. It was not possible to confirm that the trichinellosis outbreak was caused by the bacon, as none was available for testing.
Trichinellosis situation in humans:
Trichinellosis in both humans and animals is a mandatory notifiable disease in Latvia, and sporadic cases must be registered and reported. All
outbreaks are required to be reported. Since 2002, there has been a European case definition for reporting trichinellosis. The laboratory diagnosis is by testing blood serum for antibodies to Trichinella spiralis. Epidemiologists from the Public Health Agency investigate each case notified by a physician. The PHA, in collaboration with the Food and Veterinary Service (FVS), check the producers of implicated foods if there is reasonable suspicion that a business may be connected with the case. In cases of human trichinellosis due to consumption of animal products, or when the T. spiralis parasite is found in animal products and there is a potential risk of human infection, the PHA and FVS cooperate in exchanging information. In the past 7 years (1998-2004), 247 cases have been reported in Latvia. Annual case numbers peaked in 2000 with 91 cases, which included 4 outbreaks involving a total of 77 cases.
In the period 2001-2004, the number of cases reported annually has remained steady (range: 20-24), with an incidence of between 0.7 and one case per 100 000 inhabitants. In the last 5 years, cases of trichinellosis have been identified in all the age groups above one year old.
In the past 4 years (2001-2004), between one and 3 outbreaks have been identified each year involving between 2 and 20 people. In each outbreak, the epidemiological investigation has shown that the infections were due to eating infected pork.
Table 1. Outbreaks of trichinellosis in Latvia, 2000-2004:
Year / Total number of cases / Outbreaks / Total number of patients in all outbreaks
2000 / 91 / 4 / 77
2001 / 20 / 1 / 2
2002 / 20 / 3 / 13
2003 / 22 / 2 / 20
2004 / 24 / 3 / 13
Trichinellosis situation in animals:
The FVS is responsible for surveillance, reporting, and control of zoonoses in the animal population and the food chain. It has produced guidelines for slaughter houses for the veterinary examination of cows, sheep, goats and horses. Diagnosis in the FVS slaughterhouse laboratory is by trichinoscopy and compression or recovery of larvae after mechanical digestion of a sample. All pig and horse carcasses are tested for trichinella larvae. If there are any positive results, the affected slaughterhouse is investigated and placed under restrictions while legally prescribed remedial measures are instituted. When animals are slaughtered at home, or hunted for personal consumption, the owner or hunter is responsible for ensuring the carcass is tested before it is consumed.
Table 2. Epizootic situation of trichinellosis in Latvia, 1999-2004:
Tested animal species: Pigs, Wild pigs, Lynxes, Beavers, Foxes
Year / Number of checked animals / Positive cases / Number of checked animals / Positive cases / Number of checked animals / Positive cases / Number of checked animals / Positive cases / Number of checked animals / Positive cases
1999 / 368610 / - / 120 / 3 / - / - / - / - / - / -
2000 / 328546 / 3 / 238 / 5 / 2 / 2 / 5 / - / - / -
2001 / 322723 / 2 / 567 / 7 / - / - / 14 / - / - / -
2002 / 446408 / - / 583 / 9 / - / - / 8 / - / 150 / 36
2003 / 429171 / - / 313 / 13 / 2 / 2 / 8 / - / - / -
2004 / 419105 / - / 1022 / 12 / - / - / 14 / - / - / -
In the period 1999-2004, trichinellosis was identified in 3 pigs on one farm in 2000 and in 2 pigs on one farm in 2001. In each case, the pigs were slaughtered at home without veterinary supervision. Every year, trichinellosis is found in large numbers of wild pigs. To control trichinellosis outbreaks, the FVS organizes unannounced checks on food producers that have been associated with trichinellosis outbreaks. In the 1st quarter of 2005, the FVS tested 58 samples from various retail grocery products (fresh pork, 17 samples; smoked pork and bacon, 33 samples; salted bacon, 8 samples) for trichinella larvae. Trichinella larvae were not found in any of these samples.