Infectious Diseases Flashcards
Salmonella enteritidis (nontyphoidal Salmonella)
Foodborne infection (most commonly associated with eggs and egg-containing products)
Gastroenteritis - nausea, vomiting, fever, diarrhoea, cramping (may be clinically indistinguishable from other causes)
Usually occurs 8-72 hours within eating contaminated food or water
<5% develop bacteraemia - can lead to variety of extra-intestinal manifestations e.g. endocarditis, mycotic aneurysm, osteomyelitis
Salmonella meningitis is a feared complication with a high case fatality rate that occurs primarily in infants
Treatment (only if required)
- IV ceftriaxone/cefotaxime
- PO ciprofloxacin or cotrimoxazole
HIV transmission mother to child
HIV transmission rates were:
20% with no antiretroviral drugs
10% with zidovudine alone
4% on dual antiretroviral therapy
1% on 3-drug combination antiretroviral regimens
A 14-year-old boy with methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis is receiving ongoing treatment with vancomycin. Shortly after administration of his vancomycin dose, he develops diffuse erythema and hypotension. The most likely cause is:
This a description typical of red man syndrome, a well know side effect of rapid administration of vancomycin (especially well known in the oncology setting).
A four-year-old girl developed a sore throat with difficulty swallowing, dribbling, fever to 39°C, and puffiness of both upper eyelids. She was given oral penicillin V by her local doctor, but her symptoms persisted and she developed a generalised, fine, discrete, macular rash on her trunk and face. Examination showed a fever of 39.5°C, exudative tonsillitis, the macular rash, bilateral upper eyelid oedema, and generalised cervical, axillary and inguinal lymphadenitis. Her spleen could be tipped. Her chest was clear. Her photograph is shown below. Investigations show: haemoglobin 144 g/L [110-140]; white cell count 14.4 x 109/L [4-11]; platelet count 363 x 109/L [150-400]; monospot negative; urinalysis 1+ protein; serum antistreptolysin-O titre (ASOT) 479 [<200]. Which of the following is the most likely diagnosis?
Fever + tonsillitis + generalised lymphadenopathy + splenomegaly = EBV
But you usually get lymphocytosis and a positive monospot too. Monospot is specific but not very sensitive particularly at the beginning of clinical symptoms (25% false negative rate in first week, 5-10% in second week, 5% in third week).
ASOT – healthy children of primary school age commonly have titres 200-300.
EBV - fever, pharyngitis, adenopathy, fatigue and atypical lymphocytosis. There is splenomegaly (50-60% of patients) ± splenic rupture (1-2:1000). Patients can have a rash – generalised maculopapular, urticarial or petechial. The maculopapular rash almost always occurs after amoxicillin. Neuro – GBS, facial nerve palsy, aseptic meningitis, transverse myelitis. Patients can also have raised liver transaminases.
Which serological finding in patients with hepatitis B indicates active viral replication?
Hepatitis B serology: routine screening requires assay of at least 3 markers (HBsAg - surface antigen, anti-HBc, anti-HBs).
HbeAg is a marker of active viral replication and usually correlates with HBV DNA levels. HBeAg is present in active acute/chronic infections and is a marker of infectivity.
Group A streptococci cause disease in a number of ways
Suppuration, as in pharyngitis, pyoderma, or abscesses
Toxin elaboration (superantigen-mediated), as in strep toxic shock syndrome
Non-suppurative, immune-mediated inflammatory mechanisms, as in acute renal failure, acute glomerulonephritis, and, possibly, reactive arthritis
Also, only gram negative organisms can produce endotoxins and GAS is a gram +ve organism.
Hepatitis B antigens and antibodies
HBsAg
serologic hallmark of HBV infection
appears in serum 1-10 weeks after acute exposure to HBV, prior to onset of hepatitic symptoms or elevation of ALT
in patients who subsequently recover, HBsAg usually becomes undetectable after 4-6 months
persistence of HBsAg for greater than 6 months implies chronic infection
<1% of immuncompetent adults with HBV progress to chronic infection
among patients with chronic HBV, rate of clearance of HBsAg is 0.5% per year
anti-HBs
disappearance of HBsAg followed by appearance of anti-HBs
in most patients, anti-HBs persists for life
coexistence of HBsAg and anti-HBs has been reported in 24% of HBsAg +ve individuals, which implies the antibodies are unable to neutralise the circulating virions à these are regarded as carriers of HBV
HBcAg
intracellular antigen expressed in infected hepatocytes - NOT detectable in serum
anti-HBc
detected throughout the course of HBV infection
IgM anti-HBc in acute infection (although can persist for up to two years)
IgG anti-HBc persists along with anti-HBs in patients who recover from acute infection, but also persists along with HBsAg in those who progress to chronic HBV infection
HBeAg
secretory protein that is processed from precore protein
generally considered to be marker of HBV reactivity and infectivity
usually associated with high levels of HBV DNA and higher rates of infection transmission
anti-HBe
seroconversion occurs early, prior to anti-HBs seroconversion
may be delayed from years to decades in those with chronic HBV à high levels often associated with active liver disease except those who acquire the infection perinatally
seroconversion usually associated with decrease in HBV DNA and remission of liver disease
Hep B vaccination
only contains HBsAg - so will only get anti-HBs NOT anti-HBc if only vaccinated and not infected
vaccination of neonates born to HBsAg +ve mothers is most important step toward eradication of chronic HBV à HBV vaccine plus HBIG given within 12 hours of life
all other neonates follow the immunisation guidelines
patients with markers of previous infection do not need vaccination
Acute hepatitis B infection - HBsAg positive, anti-HBc positive, IgM anti-HBc positive
Chronic hepatitis B infection - HBsAg positive, anti-HBc positive, IgM anti-HBc negative
Hepatitis D superinfection - this should be suspected in a patient with chronic hepatitis B whose condition suddenly worsens
Previous hepatitis B infection - HBsAg negative, anti-HBc positive, anti-HBs positive
A three-year-old boy with beta thalassaemia presents with three days of fever to 39.5°C, and 24 hours of watery diarrhoea, colicky abdominal pain, poor oral intake and decreased urine output. He has blood transfusions every four weeks and receives a desferrioxamine transfusion six nights a week. On examination he is febrile (39.4°C) and alert but looks ill. He is not clinically dehydrated. His pulse rate is 165/minute, with a capillary refill time of 3 seconds. His respiratory rate is 32/minute. His abdomen is distended and generally slightly tender. Bowel sounds are present. His liver and spleen are both palpable 2-3 cm below the costal margin. Infection with which of the following is the most likely cause of his illness?
The patient has beta thalassaemia major (on the basis of therapy with blood transfusions every four weeks) and is also in iron overload (on the basis of chelation with desferrioxamine). Iron overload is a risk factor for Yersinia infection and therefore is the most likely infectious cause for this three year old boy’s illness.
Yersinia enterocolitica is a gram-negative coccobacilli that causes acute febrile gastroenteritis or pseudoappendicitis syndrome. It may be indistinguishable clinically from other causes of diarrhoeal illnesses (diarrhoea, abdo pain, fever plus nausea and vomiting), however in some cases pain is localised to right lower quadrant. Bloody diarrhoea is more common in children than adults. It can also cause pseudoappendicitis but at surgery, findings are of inflammation around appendix and terminal ileum and mesenteric nodes, appendix itself is generally normal. Yersinia septicaemia can occur during acute infection, particularly among infants and individuals with impaired immunity or iron-overload states.
Antimicrobial treatment is NOT recommended for acute, uncomplicated yersiniosis. The most common post-infectious sequelae are erythema nodosum and reactive arthritis (associated with HLA B27).
Serological evidence of recent streptococcal infection is LEAST likely to be associated with which of the following manifestations of rheumatic fever?
The answer is Sydenham chorea and this is because it usually presents months after streptococcal infection and therefore serological evidence is usually negative but there is usually clinical evidence of a streptococcal infection in the past.
Therefore it is least likely to be associated with serological evidence of a RECENT streptococcal infection. But the diagnosis of Sydenham chorea is a clinical diagnosis with correlating positive ASOT. It is seen in 10-15% of patients with acute rheumatic fever.
Migratory polyarthritis is seen in 75% of cases.
Carditis is seen in about 50-60% of cases.
Erythema marginatum is seen in < 3% of cases.
Subcutaneous nodules are seen in <1% of cases.
Giardia Lamblia
protozoan parasite which is common in resource poor settings. In areas where there are limited sanitation facilities and poor quality water supply, nearly half of children under five years will test positive for Giardia on stool sample but not all of these children will be symptomatic. Giardia is shed intermittently in stool so multiple samples are needed to make the diagnosis. In well-formed stool, cysts are more likely to be seen. In loose stools, trophozoites. The trophozoite is multi flagellated which gives it a beautiful kite-like appearance
Cryptosporidium Parvum
along with Giardia and Rotavirus are the most common infectious causes of diarrhoea in children worldwide. Cryptosporidium has a similar clinical presentation to Giardia but appears as a very small (4-6 micrometres) cyst in the stool which can be difficult to see (crypt = hidden). As well as being common in resource poor areas, it is associated with contaminated drinking water or swimming pools.
Tropical Sprue
chronic diarrhoeal disease that, as the name suggests, occurs in the tropics. It may also occur in visitors who spend more than two weeks (usually more than a month) in the area. It possibly has an underlying infectious cause which leads to small bowel malabsorption. Vitamin B12 and folic acid deficiency are characteristic. It is diagnosed by small bowel biopsy.
Campylobacter
acute colitis in travellers where children present with diarrhoea, acute cramping abdominal pain, mucus and bloody stools. You would expect to see gram negative curved rods or spirals on stool culture.
