Salmonellae are among the most common bacterial foodborne pathogens worldwide and the second most commonly reported zoonotic agent in the European Union (EU), with notification rates of 20.1 cases per 100,000 population in 2018 . Salmonellae caused 31% of all food- and water-borne outbreaks in the EU in 2018 . In the Czech Republic (CZ), Salmonella was the leading causative agent of acute gastroenteritis until 2006. Since 2007, it has been the second most common after campylobacteriosis .
Salmonella spp. are Gram-negative bacteria belonging to the Enterobacteriaceae family. Subspecies of species S. enterica are subdivided into more than 2500 serovars, many of which commonly colonize animals and infect humans [3, 4]. Different Salmonella serovars are also categorised as typhoidal (S. Typhi and S. Paratyphi) and non-typhoidal (e.g. S. Enteritidis, S. Typhimurium, and S. Infantis), based on causative agent and clinical symptoms . In our study, we only consider non-typhoidal human salmonellosis as this is the most burdensome class of Salmonella infections in humans within developed countries.
Salmonella usually causes gastroenteritis in humans. Systemic infections are rare . Incubation periods of Salmonella range from 6 to 72 h (most usually 12–36 h) . Salmonella bacteria tolerate various environmental conditions. They can grow at temperatures ranging from 8 to 45 °C and in pH range 4.0–9.0 . The bacteria can persist for a long time in feed mill environments .
It is estimated that 86% of human Salmonella infections are of foodborne origin . Mass production and distribution of food disseminates pathogens rapidly . The foods most commonly associated with strong-evidence salmonellosis outbreaks in Europe are eggs, bakery products, mixed food, pig meat and products thereof, and poultry meat, followed by other food vehicles including vegetables and fruits . In food, the highest levels of Salmonella-positive samples have occurred in poultry meat and other minced meat intended to be cooked before consumption . Cross-contamination may of course also occur. The most important source of human salmonellosis at the EU level during 2007–2009 was estimated to be the laying hen reservoir (i.e. eggs), followed by pigs .
Several possibilities exist for controlling Salmonella in animals. Effort to reduce Salmonella in poultry is coordinated through EU control programmes. The basic law on the control of Salmonella and other specific foodborne zoonotic agents is Regulation (EC) No 2160/2003. Monitoring of Salmonella spp. along the food chain is conducted in accordance with Regulation (EC) No 2073/2005, which lays down food safety and process hygiene criteria . Implementation of the general and specific hygiene measures is based on Regulation (EC) No 852/2002 . In the CZ, the new veterinary strategies for reduction and control of Salmonella in poultry in accordance with EU legislation were officially implemented in January 2008 (although some of these had been started 1 year earlier). These new programmes for Salmonella reduction are conducted by the Czech State Veterinary Administration, a public administrative body under the Ministry of Agriculture, and are mainly based on principles of good husbandry, implementing consistent sanitation and zoohygienic measures, and ensuring the provision of healthy feed and water. The programmes are aimed at reducing the prevalence of Salmonella in poultry and the environment and its transmission to humans via contaminated food. Four categories of poultry are monitored, including breeding stock imported from abroad and animals being produced for transport abroad. Details of the national programmes are available from the State Veterinary Administration . Mandatory vaccination is another tool for controlling the occurrence of Salmonella in poultry.
Pork is also an important source causing human salmonellosis. Eradicating Salmonella from pig farms can be both difficult and costly . Regulation (EC) No. 218/2014 requires that competent authorities evaluate the implementation of slaughterhouse operators’ own checks for presence of Salmonella in pig carcasses at slaughterhouses . Other than as described above, data of food, animals, and feedstuffs are not collected in a harmonised manner, although these do still need to be monitored in accordance with Directive 2003/99/EC on the monitoring of zoonoses . Preventive actions, including testing for Salmonella, are mainly directed to avoiding contamination at feed mills and on farms. Along with technical and hygienic measures, vaccination is another possibility to prevent Salmonella colonization in swine herds .
Higher air temperatures may lead to increased foodborne illness. Within the range 7.5–37 °C, Salmonella spp. multiply in food in direct proportion to changing temperature . In the absence of any control measures, therefore, increased air temperatures may accelerate bacterial reproduction at various points along the food chain, thus making the consequences of subsequent ingestion more severe. Air temperature may also influence people’s behaviour in ways that affect the chances for foodborne illness to occur (such as to prompt buying of ready-to-eat food or barbecuing in warmer weather) . Increased outdoor recreational activity may also increase the likelihood that people will be exposed to environmental sources of Salmonella . Many studies have demonstrated positive associations between temperature and foodborne illness in a variety of geographical settings [13,14,15,16]. Linear associations have been noted between temperature and notifications of salmonellosis in European countries and Australia .
The aim of our study was to analyse the influence of air temperature and implemented veterinary measures on salmonellosis incidence in the CZ.