Infectious Disease Flashcards
Describe the structure of gram-positive bacteria.
Gram-positive bacteria have a cell membrane (phospholipid bilayer) and a thick cell wall.
Describe the structure of a gram-negative bacteria.
Gram-negative bacteria have a cell membrane (phospholipid bilayer), thin cell wall and another phospholipid bilayer (containing lipopolysaccharides).
What is the primary stain used in gram-staining?
Crystal violet stain.
Explain why some bacteria are gram-positive and others are gram-negative.
Bacteria with thick peptidoglycan cell wall retain the crystal violet stain.
Bacteria with a thinner cell wall allow the stain to be washed out on the addition of ethanol.
Gram-negative bacteria: What is endotoxin?
The lipid component of the lipopolysaccharide cell membrane in Gram-negative bacteria is released during replication and after bacterial death… can cause septic shock.
Describe the structure of mycoplasma bacteria.
Lack a cell wall around their cell membranes.
How does the lack of a cell wall in mycoplasma bacteria determine antibiotic resistance?
Mycoplasma are resistant to antibiotics which target cell wall synthesis (cephalosporins and penicillins).
Which antibiotics target cell wall synthesis?
Cephalosporins.
Penicillins.
What shape are cocci bacteria?
Round.
Give three examples of Gram-positive cocci.
Staphylococci.
Streptococci.
Enterococci.
Give two examples of Gram-negative cocci.
Neisseria meningitidis.
Neisseria gonorrhoea.
Give examples of Gram-positive rods.
Actinomyces. Bacillus anthracis. Clostridium. Diphtheria. Listeria monocytogenes. Remember: ABCD L
Define sepsis.
Life-threatening organ dysfunction caused by dysregulated host response to infection.
Describe the pathophysiology of sepsis.
Macrophages, lymphocytes and mast cells release vast amounts of cytokines, interleukins and tumour necrosis factor.
Cytokines cause vessel endothelium to become more permeable.
Fluid leaks out of the blood and into the extracellular space.
Oedema develops and loss of intravascular volume.
Oedema reduces gass exchange between blood and tissues (low oxygen).
What blood marker is most useful in assessing sepsis (and why)?
Lactate (produced in anaerobic respiration due to hypoperfusion of tissues).
Describe pathophysiology of sepsis (coagulation).
Activation of coagulation system leads to fibrin deposition throughout the circulation.
Platelets and clotting factors are consumed during clot formation.
Leads to thrombocytopenia, haemorrhages and an inability to clot / stop bleeding.
What factors increase the risk of sepsis?
Extremes of age. Frail with multiple comorbidities. Pregnant. Trauma or surgery. Reduced immunity. Indwelling lines / catheters. Intravenous drug use. Skin infections/burns/cuts.
What scoring system can be used in sepsis assessment?
NEWS2.
At what NEWS2 score should you consider beginning the sepsis six protocol?
≥ 5
What are the sepsis six?
Administer oxygen (> 94% or 88-92% if COPD). Take blood cultures. Give broad spectrum antibiotics. Give intravenous fluid challenges. Measure serum lactate. Measure hourly urine output.
What is the management of sepsis?
If lactate > 2 or SBP < 90mmHg give 500ml intravenous fluid over 15 minutes.
Give intravenous co-amoxiclav if not penicillin-allergic.
Sepsis management: How much fluid should you give before seeking senior help?
~ 2 litres (this is a guide and you should obviously escalate sooner if needed).
What is septic shock?
Sepsis characterised by circulatory, cellular and metabolic abnormalities that substantially increase mortality.
SBP < 90mmHg.
Lactate > 4mmol/L.
What is the presentation of initial HIV infection?
Seroconversion illness 3-12 weeks after infection… short flu-like illness, sore throat, maculopapular rash, malaise, diarrhoea, mouth ulcers.
What is the presentation of established HIV infection?
Weight loss and recurrent infections.
Give examples of possible transmission routes for HIV.
Unprotected anal, vaginal or oral sexual activity.
Mother to child at any stage of pregnancy, birth or breastfeeding.
Mucous membrane, blood or open wound exposure to infected blood/bodily fluids.
AIDS: When do AIDS-defining illnesses occur?
When CD4 count has dropped to a level that allows for unusual opportunistic infections and malignancies to appear.
HIV: Give six examples of AIDS-defining illnesses.
Kaposi's sarcoma. Pneumocystis jirovecii pneumonia Cytomegalovirus infection Candidiasis (oesophageal or bronchial) Lymphomas Tuberculosis
What is Kaposi’s sarcoma?
Type of cancer that can form masses in the skin, lymph nodes, mouth or other organs.
Typically: painless, purple skin malignancies.
How is diagnosis of HIV performed?
Combination test of HIV p24 antigen and HIV antibody.
When do antibodies develop in HIV infection?
Four to six weeks following initial infection.
HIV: Other than viral load, how is the extent of disease // disease severity monitored?
CD4 count (CD4 cells are destroyed by the HIV virus and < 200 cells is considered AIDS - high risk).
HIV: Individuals with AIDS (CD4 count < 200) should receive what prophylactic therapy?
Co-trimoxazole for protection against pneumocystis jirovecii pneumonia.
What is the management of HIV?
Antiretroviral therapy.
What is MRSA?
Methicillin resistant staphylococcus aureus.
Staph. aureus resistant to beta-lactam antibiotics such as penicillins, cephalosporins and carbapenems.
How is MRSA treated?
Skin and respiratory tract are often colonised:
Antibacterial nasal creams.
Chlorhexidine body wash.
What is cellulitis?
Infection of the skin and soft tissues underneath.
Cellulitis: What should you look for on examination to find cause?
Look for skin breaches (point of entry for bacteria).
Give examples of causes of cellulitis.
Skin trauma.
Eczematous skin.
Fungal nail infections.
Ulcers.
What are the clinical features of cellulitis?
Erythema. Warm/hot to touch. Tense. Thickened. Oedematous. Bullae. Golden-yellow crusting.
Cellulitis: Define bullae.
Fluid-filled blisters.
Cellulitis: What causes gold-yellow crusting?
Staphylococcus aureus infection.
What pathogens most commonly cause cellulitis?
Staphylococcus aureus.
Group A streptococcus.
Group C streptococcus.
What is the treatment of cellulitis?
Flucloxacillin.
What is the primary differential for a person presenting with five day-history of feeling generally unwell, now has sore throat, tender lymphadenopathy and splenomegaly?
Glandular fever (infectious mononucleosis).
Infectious mononucleosis (glandular fever) is usually caused by what pathogen?
Epstein-Barr virus.
Glandular fever: How is EBV transmitted?
Oropharyngeal route in saliva (“kissing disease”)
What is the prodrome of glandular fever?
Flu-like illness (headache, low fever, chills) for three to five days.
What are the clinical features of glandular fever?
Exudative pharyngitis (sore throat), tender lymphadenopathy, splenomegaly and widespread erythematous macular rash.
What is the diagnostic triad for glandular fever?
Lymphocytosis.
> 10% atypical lymphocytes on peripheral blood film.
Positive serology for EBV.
Name an antibody test that can be performed in the investigation of glandular fever?
Monospot (mononuclear spot) test.
Glandular fever: The Monospot test detects the presence of which antibodies?
Heterophile antibodies.
Glandular fever: How is a Monospot test performed?
Patient’s blood is introduced to red blood cells from horses.
Glandular fever: What is the result of a positive Monospot test?
Reaction between heterophile antibodies and the horse red blood cells results in agglutination.
What is the management of glandular fever?
Supportive management. Advise to avoid contact sports and alcohol for one month.
Give five complications of glandular fever.
Splenic rupture. Glomerulonephritis. Haemolytic anaemia. Thrombocytopenia. Chronic fatigue.
Epstein-Barr virus is associated with the development of what cancer?
Burkitt’s lymphoma (non-Hodgkin’s lymphoma).
What pathogen causes tuberculosis?
Mycobacterium tuberculosis.
How is tuberculosis transmitted?
Tuberculosis bacteria are mostly spread by inhaling saliva droplets from infected people.
Give three risk factors for tuberculosis?
Non-UK born (e.g. South Asia).
Immunocompromised (e.g. HIV).
Close contacts with TB.
What is active TB?
Active infection after exposure to Mycobacterium tuberculosis.
What is latent TB?
The immune system encapsulates the infection to stop its progression.
What is secondary TB?
Reactivation of latent TB… such as if the patient becomes immunocompromised.
What is miliary TB?
Uncontrolled, disseminated, severe disease.
Why does Mycobacterium tuberculosis most commonly cause pulmonary TB?
M. tuberculosis has high oxygen demands.
What % of cases of TB are pulmonary?
70%
How does tuberculosis present clinically?
A history of chronic, worsening symptoms such as lethargy, fever, night sweats, weight loss, cough +/- haemoptysis.
Extrapulmonary features include lymphadenopathy (usually in neck) and erythema nodosum.
TB: What type of vaccine is BCG vaccine?
Live attenuated vaccine.
TB: Describe the level of protection offered by the BCG vaccine.
Offers protection against severe and complicated disease but is less effective at protecting against pulmonary TB.
TB: What test is performed prior to receiving the BCG vaccine?
Mantoux test.
Describe how a Mantoux test is performed.
Tuberculin (purified tuberculosis protein derivative isolated from the bacteria) is injected intradermally. Results are read/measured 72 hours later.
How is a Mantoux test interpreted?
6-15mm of induration indicates hypersensitivity (e.g. previous TB or BCG).
> 15mm induration indicates strong hypersensitivity (e.g. TB infection).
What is the gold standard test for diagnosing tuberculosis?
Sputum smear and culture.
What stain is used in a sputum smear for tuberculosis?
Zeihl-Neelsen stain.
How does Mycobacterium tuberculosis appear with Zeihl-Neelsen stain?
Bacteria are bright red against a blue background.
What does CXR reveal in primary TB?
Patchy consolidation, pleural effusions, hilar lymphadenopathy.
What does CXR reveal in reactivated TB?
Patchy/nodular consolidation with cavitation (in upper zones).
What does CXR reveal in miliary TB?
“Millet seeds” uniformly distributed throughout the lung fields.
What is the treatment of latent tuberculosis?
Three months of isoniazid (+pyridoxine) and rifampicin. OR
Six months of isoniazid (+pyridoxine).
What drug is given alongside isoniazid in the treatment of TB (and why)?
Pyridoxine is vitamin B6.
Used to prevent peripheral neuropathy, a risk of isoniazid.
What is the treatment of active tuberculosis?
Two months of rifampicin, isoniazid (+pyridoxine), pyrazinamide, ethambutol… followed by four months of rifampicin and isoniazid (+pyridoxine).
TB management: What are side effects of rifampicin use?
Orange-red discolouration of secretions (urine and tears).
TB management: What are side effects of isoniazid use?
Peripheral neuropathy.
TB management: What are side effects of pyrazinamide use?
Hyperuricaemia and subsequent gout.
TB management: What are side effects of ethambutol use?
Colour blindness and reduced visual acuity.
What is septic arthritis?
An infection that occurs within a joint (either native or joint replacement).
What is the clinical presentation of septic arthritis?
Hot, red, swollen and painful joint (often the knee). Other features include stiffness and reduced ROM. Systemic features include fever, lethargy and sepsis.
Give examples of pathogens that can cause septic arthritis?
Staphylococcus aureus (most common). Neisseria gonorrhoea. Group A Strep (Streptococcus pyogenes). Haemophilus influenzae. Escherichia coli.
Neisseria gonorrhoea septic arthritis in more likely in which group of people?
The young and sexually active.
How is septic arthritis investigated?
Aspirate the joint prior to antibiotics and send for gram-staining, crystal microscopy, culture and antibiotic sensitivities.
What is the treatment of suspected septic arthritis?
Give broad-spectrum e.g. flucloxacillin and rifampicin until the sensitivities are known
What is syphilis?
A sexually transmitted infection.
What is the route of transmission of syphilis?
Skin or mucous membranes.
What is the causative organism of syphilis?
Treponema pallidum.
What is the incubation period of syphilis?
Around 21 days from initial infection to symptoms.
Give examples of opportunities for syphilis transmission.
Oral, vaginal, anal sex involving direct contact with infected area.
Vertical transmission from mother to baby during pregnancy.
Intravenous drug use.
Blood transfusions and other transplants.
What are the three stages of syphilis infection?
Primary syphilis.
Secondary syphilis.
Tertiary syphilis.
What are the clinical features of primary syphilis?
Chancre.
Local non-tender lymphadenopathy.
Syphilis: What is chancre?
A painless ulcer at the site of contact, usually genitals.
What are the clinical features of secondary syphilis?
Systemic features… fever, lymphadenopathy, maculopapular rash, buccal ‘snail track’ ulcers and condylomata lata.
Syphilis: Where does maculopapular rash typically affect?
Trunk, palms and soles.
Syphilis: What are condylomata lata?
Painless, wart-like lesions on genitals.
What are the clinical features of tertiary syphilis?
Gummas.
Aortic aneurysms.
Neurosyphilis.
Syphilis: What are gummas?
Granulomatous skin, organ and bone lesions.
What is neurosyphilis?
Can occur at any stage of infection if the infection reaches the CNS. Features: headache, altered behaviour, dementia, paralysis, tabes dorsalis and Argyll-Robertson pupil.
Neurosyphilis: What is an Argyll-Robertson pupil?
Accommodation reflex present, pupillary reflex absent.
How is diagnosis of syphilis made?
Serology (cardiolipin tests and treponemal-specific antibody tests).
Microscopic examination of infected tissue.
What is the management of syphilis?
Deep intramuscular benzylpenicillin. Refer to genito-urinary medicine for full screening for other STIs.
What is measles?
A highly infectious disease caused by the measles virus.
What are the stages of measles presentation?
Prodromal symptoms followed by general presentation.
What are the prodromal features of measles?
Cough, coryza and conjunctivitis.
Remember: Three Cs.
What are the clinical features of measles presentation?
High fever, maculopapular rash (starts behind ears and spreads to body) and Koplik spots.
Describe the pathognomic feature of measles.
Koplik spots - white lesions on the buccal mucosa.
Give three complications of measles.
Otitis media (most common).
Pneumonia (most common cause of death).
Diarrhoea.
What is the management of measles?
Supportive (nutrition and hydration). Paracetamol and ibuprofen can provide symptomatic relief.