1. MBBS Batch17 Dr S Gokul Shankar

2. Learning Outcomes At the end of the lecture, the students should  Differentiate between food borne infections and food poisoning  Outline steps to investigate food poisoning diagnosis  Describe the source, mode of infection, general characteristics, pathogenesis, laboratory diagnosis and prevention of typhoid fever.  Distinguish ulcers of H. pylori, S. typhi E. histolytica and M. tuberculosis

3. Food-associated infections  The food may simply act as a vehicle for the pathogen (e.g. Campylobacter) or provide conditions in which the pathogen can multiply to produce numbers large enough to cause disease (e.g. Salmonella).

4.  Food poisoning is caused by consuming foods that contain toxins. These toxins can be produced by micro organisms, can occur naturally in the food (for example, in certain mushrooms) or can be a contaminant. Toxins directly affect the biological reactions taking place in the body. At sufficiently high concentrations, the effects are acute and take place a few hours after consumption. Symptoms can include nausea and vomiting. The toxins can have various origins, but the two most well known bacterial toxins are produced by Staphylococcus aureus and Clostridium botulinum. Certain toxins e.g. mycotoxins have serious long-term effects even at small concentrations. Most of these toxins are resistant to heat, so they are not eliminated by cooking.

5. Food borne infections Food borne infection  is caused by an infectious pathogens (micro organisms that cause infections) in the food.  These micro organisms multiply in the intestine. Furthermore these micro organisms release toxins that invade and damage the epithelium cells.  The consequences are stomach ache and diarrhoea within some hours or several days after eating the contaminated food.  After a few days these symptoms may disappear, but one can still excrete the germ with the stools. Such a person is called a healthy carrier.

6. Types of food poisoning Infective type Multiplication of bacteria occur in vivo e.g. Salmonella Toxic type Disease follows ingestion of food with preformed toxin e.g. Staphylococcal enterotoxin Infective-toxic type Bacteria release toxin in intestine e.g. Cl. perfringens

7. Causative agents of food poisoning Infective type Salmonella typhimurium Salmonella enteritidis Vibrio parahemolyticus Campylobacter jejuni Toxic type Staph. aureus Bacillus cereus Clostridium botulinum Infective-toxic type Clostridium perfringens

9. Salmonella – Typhoid fever  GNB, motile, peritrichous  Contaminated water and food  IP 7-8days 1week - rising fever (step-ladder pyrexia) Classically it shows a step ladder rise in the first week, with an evening rise of 2°F (1.1°C), and a morning fall of about 1°F (0.55° C). During the second week the evening temperature is about 103°- 104°F, and the morning temperature is about 101°-102°F. It then starts to fall in the 3rd week Blood 2week - rose spots, abdominal pain and splenomegaly - Serology 3week - abdominal complications of haemorrhage or perforation - Stool and urine 4week – recovery Pathogenesis and virulence factors

10. Typhoid - Diagnosis  Specimen  Routine culture media  Selective medium (DCA, XLD)  Serology ○ Widal Test, ○ Vi Agglutination test

11. Typhoid – Widal Test  STO (O - group specific Ag)  STH (H - species specific Ag)  SPAH (S.paratyphi A)  SPBH (S.paratyphi B)  Titre of 1:80 or above is considered significant (1:160 positive considered positive)  Vi – 1:10 or above is considered significant Stool examination – for carriers state - Typhoid Mary

12. Immuno- prophylaxis  Live oral Ty21a vaccine (sold as Vivotif Berna) andTy21a  Injectable Typhoid polysaccharide vaccine(sold as Typhim Vi by Sanofi Pasteur and Typherix by GlaxoSmithKline).Typhoid polysaccharide vaccine Prevention Food sanitation

13. Prevention of Food Contamination  Microorganisms grow over a wide range of Temperatures - Psychrotrophs, Mesophiles, Thermophiles, Psychroduric, Thermoduric  The Center for Science in the Public Interest has offered a simple formula "2 hours -- 2 inches -- 4 days" for ensuring left-over food safety:  Two hours: You may be tempted to stay at the table chatting and digesting, but all leftovers need to be in the refrigerator within two hours.  Two inches: Don't overload food containers. Fill them only to a depth of two inches, which will allow rapid chilling of the contents.  Four days: Eat refrigerated leftovers within three to four days, or freeze if keeping longer.

16. Overview - Objectives of investigation an epidemic are to 1. to define the magnitude of the problem in terms of time, place and person 2. to determine particular conditions and factors responsible for the epidemic 3. to identify the cause, source of infection and modes of transmission 4. to determine measures to control the epidemic 5. to make recommendations to prevent recurrence  3 can be done by history taking (using epidemiological case sheet) and by relevant investigations-this time stool/vomitus/source sampling etc -isolation of agent/serological confirmation etc

18. Laboratory diagnosis - Overview  Fecal specimens should be collected in the early stages of the diarrheal disease  Ideally before antimicrobial treatment is started  A fresh stool specimen is preferred to a rectal swab  At least 5g of feces  Immediate submission to lab. If it is not possible to be delivered to the laboratory within 2hrs of its collection  Appropriate transport medium can be used

19. Laboratory diagnosis - Overview Examination of the cellular exudate of diarrheal stools may give an indication of the organism involved: o Clumps of PMN (>50 cells per high-power field), macrophages and erythrocytes are typical of shigellosis o Smaller numbers of PMN (<20 cells per high power field) are found in salmonellosis, and invasive E. coli o In amoebic dysentery the cells are mostly degenerated (ghost cells). o Leukocytes and erythrocytes are also found in about half the cases of diarrhea due to Campylobacter spp o Few leukocytes (2–5 cells per high-power field) are present in cases of cholera, enterotoxigenic and enteropathogenic E. coli

20. Laboratory diagnosis - Overview Specimen collection, transportation & storage Direct Microscopy o Gram stain(except V.cholerae and Campylobacter) Transport medium ( Cary–Blair medium, APW) Enrichment Medium (Selenite F or tetrathionate broth) Culture ○ Blood agar ○ MacConkey agar ○ Selective medium (TCBS, XLD, DCA) Identification Serology Molecular methods - PCR

21. Vaccines:  Salmonella typhi: two typhoid vaccines currently are approved for clinical use. No available vaccine is currently suitable for distribution to children in developing countries.  Shigella organisms: three vaccines have been shown to be immunogenic and protective in field trials. Parenteral vaccines may be useful for travelers and the military, but are impractical for use in developing countries. More promising is a single-dose live- attenuated vaccine currently under development in several laboratories.  V. cholerae: oral cholera vaccines are still being investigated, and their use is recommended only in complex emergencies such as epidemics. Their use in endemic areas remains controversial. In traveler’s diarrhea, oral cholera vaccine is only recommended for those working in refugee or relief camps, since the risk of cholera for the usual traveler is very low.  ETEC vaccines: the most advanced ETEC vaccine candidate consists of a killed whole cell formulation plus recombinant cholera toxin B subunit. No vaccines are currently available for protection against Shiga toxin–producing E. coli infection.  Rotavirus: in 1998, a rotavirus vaccine was licensed in the USA for routine immunization of infants.. Other rotavirus vaccines are being developed, and preliminary trials are promising. Currently, two vaccines have been approved: a live oral vaccine (RotaTeq™) made by Merck for use in children, and GSK’s Rotarix™.

22. Ulcers  H. pylori -stomach/duodenum, peptic ulcers- chronic and usually solitary  S. typhi -ileum/colon, peyers patch ulcers, linear ulcers  E. histolytica - caecum, ascending colon, rectum, circular-flask shaped ulcers  M. tuberculosis - ileum-vertical ulcers

23. All these organisms have been introduced in Year 1 and now we expect an assignment from  on the pathogenesis of these ulcers. (How the organisms cause the ulcers, the normal histology and the pathological picture)  Dr.Rajesh and Dr.Bharathi will mark these assignments. (Marks are there! )

24. Prevention of Food Poisoning WHO ‘ten golden rules’  Food processed for safety  Thoroughly cook  Eat immediately  Store carefully  Reheat thoroughly

25. Prevention of Food Poisoning WHO ‘ten golden rules’ contd  No contact between raw & cooked  Wash hands Wash hands  Keep food preparation surfaces clean  Protect from pests  Use potable water

26. THANK YOUTHANK YOU http://emedicine.medscape.com/article/175569-overview