Salmonella typhi (typhoid enteric fever)

introduction

Salmonella are Gram negative anaerobe clinically important bacteria
certain host factors make humans particularly susceptible to infection, contracted by ingesting contaminated food or water
travellers to Asia and other regions are at risk of enteric fever, often with constipation rather than diarrhoeal illness:
- typhoid
- paratyphoid enteric fever
after crossing the intestinal epithelial layer, the bacteria replicate in macrophages in Peyer’s patches, mesenteric lymph nodes, and the spleen. The bacteria may then potentially disseminate to the lungs, gallbladder, kidneys, spleen, testes, bone, joints or central nervous system.
the bacteria predominantly reside in phagolysosomes within phagocytic cells and thus in vitro antibacterial responses do not necessarily equate with in vivo responses - hence aminoglycosides are generally not useful, furthermore, as S. typhi and S. paratyphi are obligate infections of man, there are no appropriate animal models in which to test treatment regimens.

humans are the only known carriers of Salmonella typhi
- 10% of patients recovering from typhoid fever excrete S. typhi in the stool for three months while 2-3% become chronic carriers
faecal-oral transmission from person to person in areas with poor sanitation
contaminated or nonchlorinated water
most US cases are from travel to Peru, India (30%), Pakistan (13%), Mexico (12%), Bangladesh (8%), Philippines (8%), and Haiti (5%).(Emedicine)), with risk much higher in those visiting friends or family than just being tourists.

extremes of age
- neonates have highest risk
- those under 20 years and those over 70 years also have high risk (particularly if from nursing homes)
- case fatality rate for nontyphoid is 1.3% for those over age 50 years
immunocompromised states
prior antibiotic use (alters faecal flora and increases Salmonella invasion risk)
achlorhydria (eg. neonates, proton pump inhibitors (PPIs), antacids) allows more bacteria to survive the gastric juices and enter the intestine
recent bowel surgery
malnutrition
other infections such as schistosomiasis, malaria, histoplasmosis and bartonellosis increase risk

7-10 day prodrome of headache, cough, sweating, anorexia, weakness, sore throat, malaise, abdominal pain (20-40%) and constipation (10-40%) or pea-soup diarrhoea
diarrhoea is particularly likely in neonates or the immunocompromised
prodromal symptoms plateau as fever increases in stepwise manner peaking by week 2 of illness at 39-40degC

institute isolation procedures to prevent transmission to staff and patients
iv access
FBE
U&E
LFT's
look for other common differentials:
- malaria screen if returning from endemic region
- infectious mononucleosis screen (eg. Monospot)
2 x blood cultures PRIOR to starting antibiotics (positive in 50-70%)
- note: PCR on blood has sensitivity of 85-95% when performed in 1st 5 days
stool culture
- but only +ve in 60% children and 25% of adults
consult with infectious diseases team early
antibiotic Rx:
- reduced susceptibility to fluoroquinolones is common in infections acquired in the Indian subcontinent and South-East Asia. Initial therapy for infections from these regions should be with o azithromycin or iv ceftriaxone
- iv ceftriaxone 1g bd until clinical response adequate then change to oral azithromycin or ciprofloxacin for a further 7 days¹⁾
- or, if outpatient Mx is appropriate and fever < 7 days duration, o azithromycin 20mg/kg up to 1g daily for 7 days
iv fluids if dehydrated
admit to inpatient unit, single room
watch for and Ix and Mx complications as indicated
fever may continue for another 4-6 days despite antibiotic Rx

exclusion from work and social activities should be considered for symptomatic, and asymptomatic, people who are:
- food handlers
- healthcare/daycare staff who are involved in patient care and/or child care
- children attending unsanitary daycare centers
- older children who are unable to implement good standards of personal hygiene.
the exclusion applies until two consecutive stool specimens are taken from the infected patient and are reported negative.

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