Salmonella infection and diarrheal diseases

• Acute diarrheal ailment continues to pose a major public health concern
• Salmonella spp. infection is a primary factor in acute diarrheal conditions, irrespective of implemented preventative actions
• Salmonellosis manifests clinically on a spectrum from typical gastroenteritis to severe enteric fevers, mandating immediate and suitable antibiotic therapy.
• Surveillance is needed
• Prevention and control programs also need to be improved

Keywords

• Salmonella
• Outbreak
• Prevention
• Control

Key Points

• Acute diarrheal conditions correlate with notable mortality and morbidity
• Over 2 billion individuals globally are affected by diarrheal ailments each year, per the World Health Organization
• A third of these cases are linked to foodborne sources.
• Salmonellosis is among the most prevalent foodborne infections.
• Infections stemming from Salmonella are categorized as either minor or major.
• Non-typhoid Salmonella strains lead to minor salmonellosis, marked by self-resolving diarrhea and rarely progressing to bacteremia or meningitis,.
• Typhoid fever is major salmonellosis
• Typhoid fever includes symptoms like fever, headache, malaise, and cough
• D. E. Salmon, an American bacteriologist, first discovered Salmonella in 1884
• The organism was extracted from porcine intestine.
• 80% of salmonellosis incidents are not recognized within known outbreaks, being deemed sporadic, and some remain undiagnosed.
• Salmonella nomenclature presents complexity, leading to diverse classifications
• The initial classification hinged on biochemical traits.
• The Kauffman-White classification, relying on O and H antigens, operated on a one serotype-one species basis.
• Two species are included in current Salmonella taxonomy: enterica and bongori.
• S. enterica encompasses 6 subspecies—enterica, salamae, arizonae, diarizonae, houtenae, and indica according to genome and biochemical analysis
• Subspecies are further divided into serogroups (O antigen) and serovars (H antigen), classified by antigenic characteristics
• Over 2500 serovars exist
• Current research emphasizes serotyping via molecular techniques, surpassing conventional methods through improved standardization, reproducibility, and discrimination capabilities
• Molecular methods fall into three categories: those detecting serovars based on molecular subtype and specific genomic markers, and direct methods identifying genes encoding antigens
• Molecular methods offer advantages over tradition, but they require more specialized equipment

Routes of Transmission

• The primary Salmonella reservoir is the intestine of humans and animals
• The organism has been found in reptiles and insects
• Salmonella infection sources span a wide range, with eggs, meat, dairy, vegetables, and water being most significant
• Food is the common infection source in developed nations
• It is critical to identify the food source to prevent spread
• A study in PLOS One noted an increase in cases of Salmonella infection in Australia
• Australia saw a sustained rise in cases between 2000-2013, involving both Salmonella Typhimurium and Salmonella non-Typhimurium
• Over 70% of cases were foodborne in Australia
• Water can be a contamination source
• Eggs and meat (chicken, pork) are still the main sources, but produce and fruit should be kept in mind
• Chickens and other birds can carry the microorganism
• Cases have been reported after contact with pets
• Often, the animal is asymptomatic
• Person to person transmission is possible
• Some serotypes are host specific
• S. typhi only infects humans
• About 50 serovars are causes diseases in humans and animals

Recent Salmonella Outbreaks

• Promedmail.org identified several worldwide Salmonella outbreaks
• European Outbreak of Salmonella:
  • Canada, 2015: 44 cases were reported from frozen raw breaded chicken products across 4 provinces
  • South Australia, 2016: 230 cases of salmonella traced to raw mung bean sprouts
  • New South Wales, 2016: 97 cases were traced to rockmelon
  • USA, 2016: raw meal organic shake caused 27 cases of Salmonella Virchow
  • USA, 2016: 907 cases across 40 states were caused by cucumbers, possible from Mexico
  • Japan, 2017: kindergarten outbreak resulted in 87 cases
  • Sub-Saharan Africa/ Brazil, 2017: Salmonella Typhimurium
  • Israel, 2018: tahini products caused 40 cases of Salmonella concord
  • Australia, 2018: chicken sandwiches caused 49 cases
  • Chile, 2019: sushi caused 80 cases
  • USA, 2019: Backyard poultry caused >1,000 cases across 49 states
  • USA, 2019: Fresh vegetables caused >1,000 cases across several states

Salmonella Causing Enteric Fever

• USA, 2015: raw fish caused Salmonella Paratyphi
• Pakistan/ USA, 2016: Unidentified source caused 5377 cases of XDR Salmonella Typhi
• Pakistan, 2017: water caused Salmonella typhi
• Zambia, 2017: water was the source of Salmonella typhi
• New Zealand, 2017: mussels caused Salmonella Paratyphi
• Syria, 2018: water was the source of Salmonella typhi
• India, 2018: water was the source of Salmonella typhi
• USA, 2019: Unidentified
• North Korea, 2019: Unidentified
• USA, 2020: Unidentified

European Salmonella Outbreaks

• Salmonella has decreased in Europe starting in 2007 from controls in hygiene
  • European Centre for Disease Prevention and Control (ECDC) reported a 23.6% increase due to Salmonella enteritidis in 2016
  • Salmonella Enteritidis followed by Typhimurium
• Salmonella, 2015: Macaroni and cheese and eggs, Bosnia, 200 cases
• Salmonella, 2016: cheese pasta, Greece, 56 cases
• In 2017, experts announced an Enteritidis outbreak from Poland, between Feb and November there were 196 confirmed cases Salmonella Enteritidis
• Salmonella Agona 2014-2017 269 cases possibly from cucumbers
• Infantile formula caused the Salmonella poona Poona between 2018-2019 in France, Belgium Luxembourg, 32 cases
• Salmonella group D in Romania 134 cases from fast food mayonaise

Preventing Outbreaks

• Typhoid fever is rare in Europe since most reported cases involve traveling
• Correct washing of employees' hands remains a very important action in preventing outbreaks
• A study showed a 100% reduction in Salmonella pathogens when the hands were washed properly
• Contamination with poor hand hygiene, equipment, food storage, and cooking at inappropriate temperatures lead to significant risk factors
• High standards of food security are also needed by farms
• Hygiene practices must be implemented in the food processing and preparation industry
• Adding anti-Salmonella phages to Salmonella-contaminated milk or goat cheese has led to a lower rate of contamination
• Probiotics can be useful for the prevention of Salmonella infection
• Lymphocyte activation occurs and splenocyte apoptosis decreases
• Data on Salmonella infections are not aggregated from worldwide resources
• Lack of communication and preparedness is evidenced even in the response to the SARS-CoV-2 pandemic

Conclusions

• Continuous support is need to control Salmonella outbreaks
• More rigorous preventive and control measures are necessary
• Need more public health units – surveillance is an important action