Bacteria 9 (gram -ve): Typhoid Flashcards
Which bacterium causes typhoid?
Salmonella Enterica serotype Typhi
- Paratyphi C is the only one that may also infect a variety of animals
S. typhi and S. paratyphi A, B, C are gram-negative bacilli belonging to the Enterobacteriaceae group. They are inhibited and usually destroyed by acid gastric juice. Thus those with achlorhydria or those taking a proton pump inhibitor are more at risk of infection than others. All carry O (somatic) and H (flagellar) antigens. This is the basis for the Widal test (see below). However the Vi antigen is peculiar to S. typhi and S. paratyphi C.
Humans are the sole reservoir of these organisms.
How is typhoid transmitted?
- in water and food -> faeco-oral
- Carriers: asymptomatic convalescent or chronic human carriers
- most common where sanitation is poor: indian subcontinent
Ingestion of as few as 105 bacteria can cause a low attack rate with a long incubation period. However increasing the infecting dose to 109 organisms raises the attack rate to 95% and greatly shortens the incubation period. These are far lower than the comparable figures for brucellosis.
In EF the attack rate is higher and the incubation period is shorter the greater the infective load.
It is estimated that enteric fever still affects 20–27 million people each year.
Untreated the mortality exceeds 10%.
Ingestion of sewage contaminated food or water and person-to-person transfer account for the majority of cases*. Transfer of the organism by flying insects from exposed human faeces to food also occurs. This is a real hazard if prepared food is left uncovered for any length of time, e.g. when dining out of doors, self-service or buffet meals.
Transmission via contaminated fomites has also been reported.
Note that S. typhi can live for several weeks in water, milk or dust.
*Overall, transmission is commonest where there is faeco-oral spread from a convalescent or chronic carrier. Personal hygiene in food-handlers is of the highest importance in this regard
What is the pathophysiology of typhoid?
- Enters the bloodstream via thoracic duct
- multiply inside macrophages within bone marrow, spleen, liver, gallbladder
- infected bile causes secondary invasion of the bowel , collecting in large numbers in Peyer’s patches and cuasing a strong inflammatory response
What are the clinical symptoms of typhoid?
- The one and only consistent symptom is fever that is high and sustained
- if not treated early medically, severe dehdyration can set in
First week:
A gradual onset with steadily mounting fever (‘stepwise fever’), constipation more often than diarrhoea, stepwise rise in temperature, relative bradycardia and maybe a leucopenia are typical of week one.
Second week:
This is the time when the temperature rises to >40 °C and stays high. Signs of peritonitis (ileal perforation) may occur and consciousness may be clouded. Delirium may ensue. Epistaxis, melaena and haematemesis and Rose spots are sometimes found during the second week. Classical Rose spots (1–3 mm diameter), which fade on pressure, appear in about 30% of people. They are usually found on the trunk and are easier to see in fair-skinned people. See previous question
What are serious complications of typhoid?
Most common:
- Perforation (3rd week) 2. Haemorrhage 3. Severe toxaemia
Others: G6PD pts haem. anaemia, typhoid lobar pneumonia, meningitis, abscesses, immune complex nephritis
How is typhoid best diagnosed?
- Bone marrow has a higher concentration so biopsy likely better for positive result
How do we treat typhoid?
First line: chloramphenicol, amoxicillin, co-trimoxazole
Empirical treatment third generation ceph: Ceftriaxone for 2 weeks, Azithromycin for 5 days is an alternative if disease is mild. Guidelines recommend that pts with severe typhoid are also given steroids.
What different types of carrier states exist?
- Convalescent carriers: Sheds typhoid bacilli for 3 or more months after onset of acute illness. Has no history of typhoid fever or had the disease more than 1 year previously, but has two feces or urine cultures positive for S. typhi separated by 48 hours
- Chronic carriers: smouldering infection in gallbladder or urinary tract for more than 1 year
Convalescent carriers continue to excrete the bacteria in the faeces (gall bladder) or urine (kidney) for 9–12 months after an acute attack. They are infective during this time and unless personal hygiene is good they can easily pass the disease on to others. 1–3% goes on to become chronic carriers, most commonly with persisting foci of infection in the gall bladder. The renal tract is the second commonest location. From time to time, over many years, their faeces and/or urine teem with Salmonellae. These people constitute a hazard to the community if their personal hygiene is poor or if basic sewage treatment is inadequate.
The chronic carrier should be given an extended course of an appropriate antibiotic but this is not always successful. Cholecystectomy should be considered if the gall bladder is involved.
What are the clinical features of paratyphoid A, B and C?
A and B: infection via contaminated food, diarrhoea and vomiting often precede septicaemia
C: produces septicaemia without involvement of the gut
There are many conflicting reports about the danger and incidence of paratyphoid fever. A general view is that S. paratyphi A is now almost as common as S. typhi, perhaps more common worldwide. It is transmitted in the same way and is clinically very similar to S. typhi although it has a more abrupt onset, is generally less severe and has a shorter course. Since paratyphoid is generally acquired by eating food on which the organisms have already multiplied. Diarrhoea and vomiting frequently precede septicaemia.
Treatment is the same for both typhoid and paratyphoid.
Paratyphoid is most common in teenagers while typhoid fever is most common in young children. This may be due to the fact that teenagers eat food from street vendors (transmit S. paratyphi) while household contact is more likely in the case of young children.
It is suggested the 50% of EF in tourists is now due to paratyphoid A disease. These cases often present with diarrhoea and vomiting similar to travellers’ diarrhoea. This is generally treated with an antibiotic, thus forestalling progression to typical EF septicaemia.
Like typhoid, humans can harbour paratyphoid either as faecal or urinary carriers. However it is probable that the carrier state in paratyphoid only lasts up to a year.
It is interesting to note that pre-existing S. haematobium is associated with a chronic urinary carrier state for EF.
Paratyphoid B is similar in most respects to typhoid except that gastrointestinal symptoms are more frequent in the former and that paratyhpoid is B more common in Europe than paratyphoid A.
How do we prevent typhoid from spreading and what different types of vaccines exist?
Modern intramuscular vaccine contains purified Vi antigen thus provoking antibodies against the Vi antigen of S. typhi and S. paratyphi C. Protection, at very best, is said to be about 90% (more likely about 70%) which declines rapidly over the subsequent 3 years.
The oral vaccine (Ty21a) is a live attenuated vaccine used mostly in North America. It has the advantage of also probably being effective against Paratyphoid B. Unfortunately it is expensive and the course has to be repeated anew if capsules are left out of the fridge, or if a day in the schedule is missed.
MCQ / SAQ Key words
Unspecific presentation - fever over week slowly rising to a temperature of 40 degrees
SAQ: There is a suspected outbreak of Typhoid in a community living in the outskirts of Dhaka in Bangladesh. Described how you would: a) Confirm the cause of the outbreak b) Treat suspected cases c) Control the outbreak and reduce the incidence of infection
How is non-typhoidal Salmonella different?
- Causes invasive disease in HIV+ pts with sepsis and death.
- Unlike typhoidal-salmonella which only has human reservoir – the NTS have animal reservoirs too. In the UK mass egg/meat production is responsible for a non-invasive transient enterococcal infection – in HIV+ it is invasive, unlike the typhoidal-salmonellas which are unaffected by HIV status.
- It presents as general sepsis and co-infection with bacteria/mycobacteria is common. It is the most common cause of sepsis in HIV+ pts in many parts of Sub-Saharan Africa.
- Diagnosis is blood cultures
- Treatment [prior to culture results] is as for sepsis including broad-spectrum antibiotics, screening for malaria, etc. ART if HIV+
What does the term enteric fever refer to?
The term enteric fever is used loosely but denotes any febrile systemic infection caused by Salmonella enterica serotype typhi (typhoid fever) or serotype paratyphi A, B or C (paratyphoid fever).
- about 20% mortality
