INFECTIOUS DISEASE 2 Flashcards by Eira Hegarty

Discuss initial HIV testing:

4th gen lab tests:
HIV 1&2 antibodies and p24 antigen

Window period of 45 days - the negative result is only reliable after 45 days.

Point of care test for HIV antibodies exist, results in minutes but they have a 90 day window period.

RNA viral load is useful if acute HIV infection is suspected and ab/ag test is negative

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If initial screening tests suggest HIV, what are the next line investigations to confirm it?

HIV confirmatory test - HIV1/2 antibody differentiation immunoassay

Also CD4 count and resistance testing - genotypic resistance prior to ART

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Why are Mycobacterium tuberculosis (rod) difficult to culture in a lab, and difficult to gram stain / what different stain is used?

Slow growing and big oxygen requirement

They have a waxy coating which is difficult to gram stain. Need Ziehl-Neelsen stain where they go red against a blue background. They are described as acid-fast bacilli.

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TB is mostly spread through saliva droplets. There are 4 outcomes once in the body, what are they?

Immediate clearance

Primary active TB

Latent TB

Reactivation of latent TB

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Patients with latent TB are not symptomatic and CANNOT spread the bacteria. If it is reactivated, the infection can develop. What can trigger reactivation of TB?

Immunosuppression e.g. drugs, HIV
Silicosis
CKD
Solid organ transplant
IVDU
Haematological malignancy
Anti-TNF
Gastrectomy

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Diagnosis of latent TB:

Mantoux / tuberculin skin test OR IGRA
+ CXR to exclude active TB

If skin is raised >0.5 mm, = positive, regardless of BCG history.
If active TB is excluded, consider IGRA for latent TB.

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How does the IGRA work?

Mix blood sample with antigens from M.tub bacteria.
After previous contact with M.tub, white blood cells becomes sensitised to the tuberculin antigens and release interferon gamma on further contact.
Interferon gamma detected = positive

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Diagnosis of active TB:

CXR - upper lobe cavitation, if reactivated, bilateral hilar lymphadenopathy (unilateral is more likely in primary TB).

Sputum smear - need 4 specimens. Shows acid fast bacilli. Seen in 50-80%, lower rates in HIV.

Sputum cultures = gold standard but can take 1-3 weeks to culture

NAAT is rapid

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Relative sensitivity of active TB tests:

Culture > NAAT > Smear

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What does the BCG vaccine involve?

Intraderaml injection of live atenuated myocobacterium bovis.

Created immune response, providing lasting immunity.

Protects against severe and complicated TB, but less so pulmonary TB.

Must do a mantoux test prior, and only give if negative.

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TB can present with non-specific systemic symptoms, like cough, lethargy, fever and night sweats, weight loss and lymphadenopathy. Give some more specific features it may present with:

Haemoptysis

Erythema nodosum

Spinal pain due to spinal TB (Pott’s disease)

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CXR features of primary TB, reactivated TB and disseminated miliary TB:

Primary TB :
Hilar lymphadenopathy
Patchy consolidation
Pleural effusion

Reactivated:
Bilateral hilar lymphad.
Patchy, nodular consolidation in upper zone, + cavitation

Miliary: millet seeds distributed uniformly across lng fields

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NICE guidelines specify the need for ‘deep cough’ sputum samples for TB. If these are not able to be collected, what are the 2 other options for sputum culture, and 2 further culture options:

Sputum induction with nebulised saline (careful though as TB is spread through air).

Bronchoscopy + BAL

Also blood cultures and lymph node aspiration or biopsy if none of the others are working.

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Most common cause of viral URTI:

Rhinovirus

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Conditions that may present with a recent URTI (infrequent, vs rare):

Infrequent: HSP, guttate psoriasis, subacute thyroiditis

Rare: IgA nephropathy, viral labyrinthitis, ITP in children, cystic fibrosis, post strep GN, vestibular neuronitis

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Clostridia are gram-positive, obligate anaerobic bacteria. State 4 types, and give identifying features of each:

Difficile: pseudomembranous colitis, broad spec abx. Exo + cytotoxin produced. Diarrhoea

Perfringens; alpha toxin causing gas gangrene and haemolysis. Tender oedematous skin, creps and bullae.

Botulinum; flaccid paralysis (prevents Ach)

Tetani; Spastic paralysis (prevents glycine)

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Drug causes of C.difficile:

2nd + 3rd gen cephalosporins e.g. cefuroxime, cefaximine.
+ clindamycin

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What is a classical blood marker used in C.difficile, and what can it be used for, also what do you test for for diagnosis?

White cell count is raised.
Can be used to indicate severity.

Moderate >15, 3-5 stools a day

Severe >15

Stool toxin test is key. Antigen will not define current infection.

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Life-threatening features of C.Diff:

Hypotension
Partial / complete ileus
Toxic megacolon / ct evidence

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Severe features of C.Diff:

WCC >15 or actuely raised 1.5x baseline
>38.5
Severe colitis on XR / CT

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First episode of C.difficile management, 1st , 2nd and 3rd line:

Oral vancomycin 10 days
oral fidaxomycin
oral vanc +/- IV metronidazole

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Management of recurrent episode of C.difficile:

If <12 weeks then ORAL FIDAXOMYCCIN

If >12 weeks then give oral vanc or oral fidaxomycin

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Management of life-threatening C.difficile infection:

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Oral vancomycin and IV metronidazole

3 Ms of herpes simplex pap smear features:

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Multinucleated

Moulded nuclei

Migration of chromatin

When is an elective CS advised in reference to herpes?

If there has been a primary attack after 28 weeks If it is a recurrent attack, then suppressive therapy is required and the risk is low, so no CS required.

Most common cause of encephalitis, which area of the brain does it most likely affect + likely symptoms:

HSV1 Temporal lobe Aphasia (Wernicke's, nonsensical but fluent speech). Difficulty recognising faces Visual = superior homonymous quandrantanopia Fever, headache, vomiting, seizure, psychiatric symptoms?

Investigating suspected HSV encephalitis:

CSF show lymphocytosis and increased protein Viral PCR of CSF MRI is better than CT EEG would show lateralised periodic discharge

Herpes zoster ophthalmicus describes reactivation of the varicella-zoster virus in the area supplied by which nerve?

Trigeminal - ophthalmic division.

HZO presents as a vesicular rash around the eye. What sign would indicate high likelihood for developing ocular involvement?

Hutchinson's sign - rash on side or tip of the nose / nasociliary involvement.

Management of HZO:

Oral antiviral 7-10 days, started within 72 hours. + TOPICAL STEROIDS IF EYE INVOLVEMENT

Complications of HZO:

Conjunctivitis , keratitis, episcelritis and anterior uveitis. Also ptosis and post herpetic neuralgia

Investigation of choice in genital herpes, which present with painful genital ulceration +/- dysuria and pruritis, with the primary infection sometimes including headache, fever, malaise. Tender inguinal lymphadenopathy and urinary retention can sometimes occur.

NAAT testing first line. Genital = HSV2

Management of primary genital herpes <28 weeks, or recurrence of genital herpes in pregnancy:

Prophylactic aciclovir from 36 weeks

Which virus may present atypically in the fact that it will present with a low CSF glucose compared to other viruses in meningitis:

MUMPS Mumps (RNA paramyxovirus) will have a low CSF glucose, unlike other viruses which may be normal.

When should an LP be delayed in the investigation / management of meningitis?

Severe sepsis Rapidly evolving rash Severe respiratory or cardiac compromise Significant bleeding risk Raised ICP (papilloedema, GCS <=9, focal neurology, uncontolled seizure)

If an LP cannot be done within the first hour, it should be delayed and IV antibiotics should be started straight away. Which antibiotic should be given in which situation?

<3 months = cefotaxime and amox / ampicillin 3 months - 60 years = ceftriaxon 60 or over = ceftriaxone plus amox or ampicillin + vanc if recent / prolonged antibitoic use + IV dexamethasone

Antibiotic for listeria;

IV amox / amp + gent

If the patient has a history of immediate hypersensitivity reaction to penicillin or cephalosporins, which abx should be used?

Chloramphenicol

Who should be offered antibiotic prophylaxis and what should they get (if exposed to confirmed bacterial meningitis):

Exposure prophylaxis is only required with meningococcal disease. Oral ciprofloxacin or rif If had any contact within the last 7 days of the confirmed case onset. Also offer vaccination / booster.

Senior review is indicated if any of the following warning signs are present:

Rapidly progressive rash Poor peripheral perfusion RR <80 / >30 Pulse rate <40 / >140 pH <7.3 WBC <4 Lactate >4 GCS <12 or drop of 2 points Poor response to fluid resuscitation

Most common traveller's diarrhoea:

E.coli

Causes of gastroenteritis by incubation period:

1-6 hours - bacillus cereus, staph aureus 12-48 hours - salmonella, e.coli (watery, cramps, nausea) 48-72 hours - Shieglla (bloody), campylobacter (GBS, flu prodrome, ?bloody. ?looks like appendicitis)

Salmonella typhi and paratyphi is transmitted by the faeco-oral route, and also contaminated food and water. Give some clinical features, and differentiators between typhi and paratyphi:

Headache Fever Arthralgia Relative bradycardia Constipation ! in typhoid Rose spots in 40% of patients with paratyphi

Complications of typhoid:

Osteomyelitis Gi bleed Meningitis Cholecystitis Chronic carriage in 1%

Incubation period of typhoid is between 5-21 days. What does this depend on?

Age Gastric acidity Immune status Infectious load

Dengue fever is a viral infection that can progress to ? Other causes of this complication include yellow fever and ebola.

Viral haemorrhagic fever

Describe some symptoms of dengue fever:

'Break bone' fever e.g. bone pain, arhtralgia, myalgia, fever Retroirbital headahce Rash

'Warning signs' in dengue fever before it progresses to dengue haemorrhagic fever (DIC with thrombocytopenia and spontaneous bleeding):

Abdominal pain Hepatomegaly Persistent vomiting Fluid accumulation e.g. ascites , pleural effusion

A patient experiences a sudden onset of high fever, rigors, nausea and vomiting. They have a brief remission and then jaundice, haematemesis and oliguria occurs. What are they likely suffering from?

Yellow fever

Primary vs secondary vs tertiary features of syphilis:

Primary: Chancre, painless ulcer at site of sexual contact, may be on cervix in women + non tender lymphadenopathy Secondary: systemic including fever, and lympadenopathy, snail trail buccal mucosa, rash, condylomata lata. 3: gumma, argyll robertson pupil, ascending aortic aneuryms,

Treponema pallidum cannot be grown on artificial media - how is syphilis tested for and what might the results of the combinations of tests indicate?

Non-trep and trep tests +ve +ve = active infection +ve nontrep, -ve trep = false positive -ve nontrep, +trep = successfully treated syphilis

Causes of false positive non-treponemal (cardiolipin) tests:

Pregnancy Leprosy SLE APS TB HIV Malaria

Mnemonic for features of an Argyll-Robertson pupil is ARPPRA:

Accommodation Reflex Present Pupillary Reflex Absent

Management of threadworms, and species name:

Enterobius vermicularis Mebendazole, all members of household

Mx Lyme disease:

Doxycycline Amoxicillin if contraindicated e.g. pregnancy Treat straight away if erythema migrans rash is present. Investigations = ELISA test first line for Borrelia burgdorferi.

Management of latent TB:

1. 3 months of isoniazid (+pyridoxine) + rifampicin (<35, if hepatotoxicity is a concern) 2. 6 months of isoniazid + pyridoxine - if senstivity to rifamycins / interaction e.g. HIV or transplant

Investigating lyme disease:

Investigations = ELISA test first line for Borrelia burgdorferi. if -ve and within 4 weeks, and still lcinical suspicion, then repeat 4-6 weeks after initial ELISA test. Positive, then confirm with immunoblot test.

INFECTIOUS DISEASE 2 Flashcards

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