Infectious Diseases Flashcards
What are the typical incubation periods for the main causes of gastroenteritis?
1-6 hrs: Staphylococcus aureus, Bacillus cereus
12-48 hrs: Salmonella, Escherichia coli
48-72 hrs: Shigella, Campylobacter
> 7 days: Giardiasis, Amoebiasis
Mycoplasma pneumoniae is a cause of atypical pneumonia which often affects younger patients.
Describe:
1. key features
2. complications
3. investigation
4. tx
Features:
prolonged and gradual onset
flu-like symptoms classically precede a dry cough
bilateral consolidation on x-ray
Complications:
- haemolytic anaemia, thrombocytopenia
- erythema multiforme, erythema nodosum
- meningoencephalitis, Guillain-Barre syndrome and other immune-mediated neurological diseases
- bullous myringitis: painful vesicles on the tympanic membrane
Investigation: serology - positive cold agglutination test
Tx: doxycycline or a macrolide (e.g. erythromycin/clarithromycin)
Describe the key features of amoebic dysentry. How is it treated?
profuse, bloody diarrhoea
there may be a long incubation period
stool microscopy may show trophozoites if examined within 15 minutes or kept warm (known as a ‘hot stool’)
treatment is with metronidazole
Describe the key features of an amoebic liver abscess
usually a single mass in the right lobe (may be multiple). The contents are often described as ‘anchovy sauce’
features: fever, RUQ pain
serology is positive in > 90%
A history of IV drug use coupled with a descending paralysis, diplopia and bulbar palsy is characteristic of infection with…
Clostridium botulinum
- gram positive anaerobic bacillus
typically seen in canned foods and honey
prevents acetylcholine (ACh) release leading to flaccid paralysis
Tx is early antitoxin
How is cellulitis diagnosed? How is it classified?
The diagnosis of cellulitis is clinical. No further investigations are required in primary care. Bloods and blood cultures may be requested if the patient is admitted and septicaemia is suspected.
Eron classification
Describe C. perfringens infection
produces α-toxin, a lecithinase, which causes gas gangrene (myonecrosis) and haemolysis
features include tender, oedematous skin with haemorrhagic blebs and bullae. Crepitus may present on palpation
Describe C. tetani infection
produces an exotoxin (tetanospasmin) that prevents the release of glycine from Renshaw cells in the spinal cord causing a spastic paralysis
Diphtheria is caused by the Gram positive bacterium Corynebacterium diphtheriae.
How does it present? How is it treated?
Possible presentations:
- recent visitors to Eastern Europe/Russia/Asia
- sore throat with a ‘diphtheric membrane’ - grey, pseudomembrane on the posterior pharyngeal wall
- bulky cervical lymphadenopathy (‘bull neck’ appearanace)
- neuritis e.g. cranial nerves
- heart block
Management:
-intramuscular penicillin
-diphtheria antitoxin
Typhoid and paratyphoid are caused by Salmonella typhi and Salmonella paratyphi (types A, B & C) respectively.
What are the key features of the infection?
- relative bradycardia
- abdominal pain, distension
- constipation: although Salmonella is a recognised cause of diarrhoea, constipation is more common in typhoid
- rose spots: present on the trunk in 40% of patients, and are more common in paratyphoid
What is Hairy leukoplakia?
an EBV-associated lesion on the side of the tongue, and is considered indicative of HIV
Spot diagnosis:
Common amongst travellers
Watery stools
Abdominal cramps and nausea
E. coli
Spot diagnosis:
Ongoing non-bloody diarrhoea, lethargy, bloating, flatulence, steatorrhoea +/- recent travel
Giardiasis
Spot diagnosis:
Profuse, watery diarrhoea (‘rice water’)
Severe dehydration resulting in weight loss
Not common amongst travellers
Cholera
Spot diagnosis:
Bloody diarrhoea
Vomiting and abdominal pain
Fever
Shigella
Spot diagnosis:
A flu-like prodrome followed by crampy abdominal pains, fever and diarrhoea which may be bloody
May mimic appendicitis
Complications include Guillain-Barre syndrome
Campylobacter
Spot diagnosis:
Two types of illness are seen
vomiting within 6 hours, stereotypically due to rice
diarrhoeal illness occurring after 6 hours
Bacillus cereus
Spot diagnosis:
Gradual onset bloody diarrhoea, abdominal pain and tenderness which may last for several weeks
Amoebiasis
Gonorrhoea is caused by the Gram-negative diplococcus Neisseria gonorrhoae.
How does it present differently in men and women?
What local complications can arise?
males: urethral discharge, dysuria
females: cervicitis e.g. leading to vaginal discharge
Local complications that may develop include urethral strictures, epididymitis and salpingitis
What is the major systemic complication of gonorrhea? How does it present?
Disseminated gonococcal infection (DGI)
Initially there may be a classic triad of symptoms: tenosynovitis, migratory polyarthritis and dermatitis.
Later complications include septic arthritis, endocarditis and perihepatitis (Fitz-Hugh-Curtis syndrome)
It is the most common cause of septic arthritis in young adults
How is gonorrhea treated?
The first-line treatment is a single dose of IM ceftriaxone 1g
(But if the organism is sensitive to ciprofloxacin then oral ciprofloxacin 500mg should be given)
if ceftriaxone is refused (e.g. needle-phobic) then oral cefixime 400mg + oral azithromycin 2g should be used
How does Pneumocystis jiroveci pneumonia present?
How is it treated?
Who should be given prophylaxis against it?
Common presentation: new-onset, dry cough, dyspnoea and desaturation on mobilisation on a background of AIDS
CXR often clear
treated with co-trimoxazole, which is a mix of trimethoprim and sulfamethoxazole
All patients with a CD4 count lower than 200/mm3 should receive prophylaxis against PJP
How should genital herpes in pregnancy be managed?
Elective C-section at term is advised if a primary attack of herpes occurs at greater than 28 weeks gestation (3rd trimester)
Oral aciclovir 400 mg TDS (three times daily) should be taken until delivery
Women with recurrent herpes who are pregnant should be treated with suppressive therapy and be advised that the risk of transmission to their baby is low
How does infectious mononucleosis (glandular fever) present?
How is it diagnosed?
How is it managed?
Classic triad:
1. sore throat
2. lymphadenopathy: may be present in the anterior and posterior triangles of the neck, in contrast to tonsillitis which typically only results in the upper anterior cervical chain being enlarged
3. pyrexia
Diagnosis:
FBC and Monospot test (heterophil antibody test) in the 2nd week of the illness to confirm diagnosis of glandular fever
Management is supportive
Contact sports should be avoided for 4 weeks
avoid alcohol
Leptospirosis is caused by the spirochaete Leptospira interrogans, classically being spread by contact with infected rat urine.
Who is at risk?
How does it present?
Tx?
sewage workers, farmers, vets, returning travellers
the early phase is due to bacteraemia and lasts around a week (often mild):
- fever and flu-like symptoms
- subconjunctival suffusion (redness)/haemorrhage
second immune phase may lead to more severe disease:(Weil’s disease)
- acute kidney injury (seen in 50% of patients)
- hepatitis: jaundice, hepatomegaly
- aseptic meningitis
Tx is high-dose benzylpenicillin
Cause of necrotising fasciitis?
How is it treated?
type 1 (most common) is caused by mixed anaerobes and aerobes (often occurs post-surgery in diabetics).
type 2 is caused by Strep. pyogenes
urgent surgical referral debridement
intravenous antibiotics
What type of pneumonia does influenza predispose to?
Staph aureus pneumonia
Schistosomiasis, or bilharzia, is a parasitic flatworm infection.
How does it present?
Investigation?
Tx?
- ‘Swimmer’s itch’
- urinary frequency and haematuria
- bladder calcification
- eosinophilia
Investigation:
- for asymptomatic patients serum schistosome antibodies are generally preferred
- for symptomatic patients the gold standard for diagnosis is urine or stool microscopy looking for eggs
Tx: single oral dose of praziquantel
The risk of overwhelming post splenectomy infection (OPSI) is greatest in the first two years following splenectomy.
Which organisms commonly cause it?
What abx prophylaxis should be given?
Streptococcus pneumoniae
Haemophilus influenzae
Meningococci
Penicillin V
Pneumococcal vaccination is also offered
Ideally 2 weeks before surgery
What are the complications of a splenectomy?
Haemorrhage (may be early and either from short gastrics or splenic hilar vessels)
Pancreatic fistula (from iatrogenic damage to pancreatic tail)
Thrombocytosis: prophylactic aspirin to mitigate
Encapsulated bacteria infection e.g. Strep. pneumoniae, Haemophilus influenzae and Neisseria meningitidis
What blood film changes are seen post-splenectomy?
Platelets will rise first (therefore in ITP should be given after splenic artery clamped)
Blood film will change over following weeks, Howell-Jolly bodies will appear
Other blood film changes include target cells and Pappenheimer bodies
What is the diagnostic criteria for staphylococcal toxic shock (TSS)?
How is it treated?
fever: temperature > 38.9ºC
hypotension: systolic < 90 mmHg
diffuse erythematous rash (w/ desquamation of rash, especially of the palms and soles)
involvement of three or more organ systems: e.g. GI (D+V), mucous membrane erythema, renal failure, hepatitis, thrombocytopenia, CNS involvement (e.g. confusion)
Tx: removal of infection focus (e.g. retained tampon)
IV fluids + abx
How is asymptomatic bacteriuria in pregnancy managed?
Immediate tx with abx
Define septic shock
a subset of sepsis with profound circulatory, cellular and metabolic abnormalities, associated with greater risk of mortality than sepsis alone
Give some causes of fever in a returned traveller
0-10 days: Dengue, rickettsia, viral (including infectious mononucleosis), gastrointestinal (bacteria / amoeba)
10-21 days: Malaria, typhoid, primary HIV infection
> 21 days: Malaria, chronic bacterial infections (e.g. brucella, coxiella, endocarditis, bone and joint infections); TB; parasitic infections (helminths/protozoa)
Falciparum malaria is the commonest, and most severe, type of malaria. Describe the key presenting features
Feature of severe malaria:
schizonts on a blood film
parasitaemia > 2%
hypoglycaemia
acidosis
temperature > 39 °C
severe anaemia
What are the major complications of severe falciparum malaria?
hypoglycaemia
cerebral malaria: seizures, coma
acute renal failure: blackwater fever, secondary to intravascular haemolysis, mechanism unknown
acute respiratory distress syndrome (ARDS)
disseminated intravascular coagulation (DIC)
shock may indicate coexistent bacterial septicaemia - malaria rarely causes haemodynamic collapse
First line tx for uncomplicated falciparum malaria?
WHO guidelines recommend artemisinin-based combination therapies (ACTs) as first-line therapy
examples include artemether plus lumefantrine, artesunate plus amodiaquine, artesunate plus mefloquine
First line tx for complicated falciparum malaria?
a parasite counts of more than 2% will usually need parenteral treatment irrespective of clinical state
- IV artesunate or Iv quinine dihydrochloride
if parasite count > 10% then exchange transfusion should be considered
What is the most common cause of non-falciparum malaria?
Plasmodium vivax
How does non-falciparum malaria present?
general features of malaria: fever, headache, myalgia, anaemia, hepatosplenomegaly, jaundice
Plasmodium vivax/ovale: cyclical fever every 48 hours. Plasmodium malariae: cyclical fever every 72 hours
Plasmodium malariae: is associated with nephrotic syndrome.
Ovale and vivax malaria have a hypnozoite stage and may therefore relapse following treatment.
How should non-falciparum malaria be treated?
in areas which are known to be chloroquine-sensitive then WHO recommend either an artemisinin-based combination therapy (ACT) or chloroquine
in areas which are known to be chloroquine-resistant an ACT should be used
ACTs should be avoided in pregnant women
patients with ovale or vivax malaria should be given primaquine following acute treatment with chloroquine to destroy liver hypnozoites and prevent relapse
How is a diagnosis of malaria made?
malaria blood film - sent in an EDTA bottle (red)
Need 3 samples over 3 consective days to exclude malaria due to 48 hour lifecyle
can also do:
FBC, U&Es, LFTs, glucose, coagulation
CT head
What anti-malarials can be offered to travellers?
Proguanil and atovaquone (malarone)
- 2 days before, daily and 1 week after
mefloquine
- once weekly 2 weeks before, during and 4 weeks after
- can cause psychosis
Doxycycline
The lungs remain the most common site for secondary tuberculosis. Where may extra-pulmonary infection affect?
central nervous system (tuberculous meningitis - the most serious complication)
vertebral bodies (Pott’s disease)
cervical lymph nodes (scrofuloderma)
renal
gastrointestinal tract
How is TB investigated?
The Mantoux test is the main technique used to screen for latent tuberculosis. (interferon-gamma blood test may be used if risk of false negatives)
Chest x-ray
upper lobe cavitation is the classical finding of reactivated TB
bilateral hilar lymphadenopathy
Sputum smear
3 specimens are needed, rapid and inexpensive
stained for the presence of acid-fast bacilli (Ziehl-Neelsen stain)
all mycobacteria will stain positive (i.e. nontuberculous mycobacteria)
Nucleic acid amplification tests (NAAT)
allows rapid diagnosis (within 24-48 hours)
more sensitive than smear but less sensitive than culture
Sputum culture
the GOLD STANDARD investigation
more sensitive than a sputum smear and nucleic acid amplification tests
can assess drug sensitivities
can take 1-3 weeks
