Salmonellosis

Salmonellosis is a food-borne disease caused by Salmonella bacteria, and one of the most common diarrhoea-causing diseases in Europe. Contaminated eggs or egg products carry the highest risk of infection. Although large salmonellosis outbreaks often attract media attention, most cases are sporadic and not part of a large outbreak. Since 2014, Salmonella infections are reported to occur annually in 30 European countries and the overall notification rate in Europe was 16.6 per 100 000 people in 2021 (ECDC, 2016-2023). Global warming and an increase in extreme weather events are likely to increase the prevalence and spread of food-borne diseases like Salmonellosis.

Source & transmission

Salmonella bacteria are widely present in food-producing and wild animals. Several serotypes of the Salmonella e. enterica subspecies that can make people sick can be transmitted from animals to humans (Rabsch et al., 2002). The bacteria are resistant and can survive several weeks in a dry environment or even several months in water. Infections are sometimes invasive and can be life threatening.

Mostly, humans get salmonellosis via consumption of contaminated food of animal origin (mainly eggs, but also milk, meat, and poultry). However, also raw vegetables can be a source of infection when contaminated by animal faeces or cross-contaminated during food preparation. Person-to-person transmission also occur after ingesting faecal contamination. Humans can also get infected via contact with living infected animals, including pets, who may not show signs of disease (Silva et al., 2013).

Health effects

Most people with a Salmonella infection suffer from only mild symptoms and recover within a few days to weeks without treatment. Usually, it is a typical gastrointestinal illness associated with diarrhoea, abdominal cramps, joint pain, headache, vomiting and a sudden onset of fever. Health effects start hours to days after ingestion of Salmonella bacteria and lasts several days to a week. In rare, severe cases, the disease can progresses to blood poisoning or persistent gastrointestinal symptoms or even a fatal outcome if the bacteria penetrate the intestinal wall and cause inflammation and fluid secretions (Lönnermark et al., 2015; WHO, 2022).

Morbidity & mortality

In the EEA member countries (excluding Switzerland and Türkiye due to absence of data), in the period 2007-2021:

• 1,334,344 infections
• Moderate probability of hospitalisation^[1]
• 985 reported fatal cases and an overall mortality rate of 0.18% in the period 2021-2022. However, in severe salmonellosis cases, the fatality rate can rise to 17% (Marchello et al., 2022).
• Stable number of cases in the period 2011-2019. In 2020, the number of cases dropped drastically, but this may be confounded by Covid-19 regulatory measures and potential underreporting. The overall notification rate in 2021 was 16.6 cases per 100 000 population.

(ECDC, 2016-2023; ECDC, 2023)

Distribution across population

• Age group with the highest disease incidence in Europe: 0 - 4 years old (ECDC, 2016-2023)
• Groups at risk of severe disease course: young children (below the age of 4), the elderly or people with a weakened immune system
  
  

Climate sensitivity

Climatic Suitability

Salmonella bacteria grow well in a wide pH range (4 to 9) and a wide temperature range (5 to 45°C), although growth is optimal between 35 and 37°C. The bacteria do not grow in standing water but need a minimal flow rate of 0.8 mL/min for its survival, while the optimal flow rate lies between 0.96 and 0.99 mL/min (Tajkarimi, 2007).

Seasonality

In Europe, infections occur year-round but peak in August and September (ECDC, 2016-2023).

Climate Change Impact

Global warming and an increase in extreme weather events have been associated with an increasing incidence of food-borne diseases. Higher air temperatures result in faster growth of Salmonella bacteria and in increased Salmonella concentrations in the food supply chain. Specifically, a one-degree temperature increase above 5°C causes 5-10% more Salmonella infections (Semenza and Menne, 2009; Kovats et al., 2004). In England, Poland, the Netherlands, the Czech Republic and Spain, more than 30% of increased disease burden could be linked to temperature effects (Semenza and Menne, 2009). Floodwaters can carry Salmonella bacteria from various sources such as sewage, animal waste, and soil and contaminate cropped areas. If contaminated crops are not properly washed or cooked before consumption, this can increase the risk of Salmonella infections. By the end of the 21^st century, climate change could increase the number of temperature-related Salmonella cases in Europe by up to 40 000 (on top of any increase expected from population changes alone) (Watkiss and Hunt, 2012).

Prevention & Treatment

Prevention

• Good sanitary hygiene on farms and in slaughterhouses to minimize faecal contamination
• Efficient sanitary practices in meat processing industries and domestic kitchens
• Cooking and/or pasteurizing raw food with a risk of infection
• Limiting or carefully supervising contact between infants, young children and pet animals
• Prevention of environmental transmission, e.g., by preventing run-off from contaminated land to reach waters used for irrigation or recreational purposes
• Surveillance of foodborne diseases to allow for disease detection and subsequent response measures to prevent spreading of the disease
• Awareness raising about disease transmission

Treatment

• Electrolyte replacement in severe cases
• Antibiotics for infants, elderly or patients in poor health, or for severe cases; for mild or moderate cases in otherwise healthy patients antibiotics are not recommended to avoid antimicrobial resistance to drugs

Links to further information

• ECDC Annual Epidemiological Reports (AERs)
• ECDC Surveillance Atlas of Infectious Diseases
  ECDC Factsheet about salmonellosis

References

ECDC, 2016-2023, Annual epidemiological reports for 2014-2021 – Salmonellosis. Available at https://www.ecdc.europa.eu/en/infectious-diseases-and-public-health/salmonellosis/surveillance-and. Last accessed August 2023.

ECDC, 2023, Surveillance Atlas of Infectious Diseases. Available at https://atlas.ecdc.europa.eu/public/index.aspx. Last accessed August 2023.

Kovats, R. S., et al., 2004, The effect of temperature on food poisoning: a time-series analysis of salmonellosis in ten European countries, Epidemiology & Infection 132(3), 443-453. https://doi.org/10.1017/S0950268804001992

Lönnermark, E., et al., 2015, Effects of Probiotic Intake and Gender on Nontyphoid Salmonella Infection, Journal of Clinical Gastroenterology 49(2), 116–123. https://doi.org/10.1097/MCG.0000000000000120

Marchello, C. S., et al., 2022, Complications and mortality of non-typhoidal salmonella invasive disease: a global systematic review and meta-analysis, The Lancet Infectious Diseases 22(5), 692-705. https://doi.org/10.1016/S1473-3099(21)00615-0

Rabsch, W., et al., 2002, Salmonella enterica Serotype Typhimurium and Its Host-Adapted Variants, Infection and Immunity 70(5), 2249–2255. https://doi.org/10.1128/IAI.70.5.2249-2255.2002

Semenza, J. C., and Menne, B.,2009, Climate change and infectious diseases in Europe, The Lancet Infectious Diseases 9(6), 365–375. https://doi.org/10.1016/S1473-3099(09)70104-5

Silva, C., et al., 2013, One Health and Food-Borne Disease: Salmonella Transmission between Humans, Animals, and Plants, Microbiology Spectrum - American Society for Microbiology Press 2(1), 1-9. https://doi.org/10.1128/microbiolspec.OH-0020-2013

Tajkarimi, M., 2007, Salmonella spp. California Department of Food and Agriculture Report PHR 250, B6, 1–8. Available at https://www.cdfa.ca.gov/ahfss/Animal_Health/PHR250/2007/25007Sal.pdf

WHO (2022). World Health Organization, https://www.who.int/. Last accessed August 2022.

[1] Hospitalisation probability is labeled as low, moderate or high when respectively < 25%, 25-75% or > 75% of cases are hospitalized.