CP theme 1

Question 1

Staphylococcus aureus

Answer 1

Gram + cocci
30-50% people carry in their nose
Able to adhere to damaged skin, produces exoenzymes and toxins that can damage tissue and promote host responses.
Commonest cause of skin and soft tissue infections.

Question 2

Staphylococcus epidermis

Answer 2

Opportunistic pathogen
Coagulase negative staphylococci
Adheres to plastics and metal using glycocalyx biofilms
Infections of foreign bodies (prosthetic devices, IV catheters etc)

Question 3

Streptococcus pyogenes

Answer 3

Gram + cocci
Group A Strep
Pharynx
Sore throat, scarlet fever, necrotising fasciitis, puerperal sepsis
Also associated with secondary immunological presentations eg. glomerulonephritis

Question 4

Streptococcus pneumoniae

Answer 4

Pharynx

Can cause other common childhood presentations eg. Otitis media Bacterial pneumonia and meningitis

Question 5

Escherichia coli

Answer 5

Gram - bacilli
Colonises in colon
Other species of coliform eg. Klebsiella pneumoniae, Enterobacter cloacae, cause similar infections
Able to adhere to uroepithelial cells/urinary catheter
Intra-abdominal infections, sepsis, haemolytic uraemia syndrome, diarrhoea
Commonest cause of UTIs

Question 6

Pseudomonas aeruginosa

Answer 6

Gram – bacilli
Present in water, opportunistic pathogen
Multi-resistant
Characteristic green pigment	
Ventilator associated pneumonia and bacteraemia

Question 7

Neisseria meningitidis

Answer 7

Gram – diplococci
Classis presentation is purpuric non-blanching rash
Reduction in cases since vaccination
Meningeal sepsis and meningitis

Question 8

Neisseria gonorrhoea

Answer 8

Gram - diplococcus
Gonorrhoea, ophthalmia neonatorum
Rarely, can cause invasive infections secondary to STIs

Question 9

Haemophilus influenzae

Answer 9

Gram – bacillus
Pharynx
Reduction in cases since Hib vaccine	
Respiratory tract infections
Capsulated types are associated with epiglottitis and meningitis.

Question 10

Clostridium

Answer 10

Anaerobes – grow in absence of oxygen, spore forming
C. difficile: Antibiotic associated diarrhoea
C. perfringens: Gas gangrene
C. tetani: Tetanus

Question 11

Mycobacterium tuberculosis

Answer 11

Does not stain with conventional Gram staining

Tuberculosis

Question 12

Chlamydia trachomatis

Answer 12

Does not have conventional cell wall

STI (Chlamydia)

Question 13

Mycoplasma pneumoniae

Answer 13

Does not have conventional cell wall

Respiratory tract infections

Question 14

Treponema

Answer 14

Spirochaetes
(other spirochaetes cause leptospirosis and Lyme disease)
Syphilis

Question 15

Herpes simplex virus 1

Answer 15

HSV – 1, cold sores
Direct contact with vesicle fluid from lesions
Latency in sensory nerve ganglion (periodic reactivatons) Vesicles/ulcers to skin or mucus membranes (typically mouth)
Encephalitis – brain inflammation, often severe or fatal

Question 16

Herpes simplex virus 2

Answer 16

Primary/first infection = chicken pox
Secondary/ reactivation = herpes zoster or shingles
Respiratory droplet or direct contact with vesicle fluid
Latency established in dorsal root ganglia of whole CNS
Chicken pox – widespread vesicular rash
Shingles/herpes zoster – unilateral vesicles in a dermatomal distribution

Question 17

Herpes Epstein Barr virus

Answer 17

Transmission by saliva and genital secretions (kissing disease)
Latency in B cells
Infectious mononucleosis (primary) – tonsillitis, fever, lymphadenopathy, hepatosplenomegaly. Atypical lymphocytes on blood film (look like monocytes).
Reactivation -> if unwell/immunosuppressed, associated with B cell lymphoproliferative disorders

Question 18

Herpes Cytomegalovirus

Answer 18

Transmission by: saliva or genital secretions, donated blood, stem cells or solid organs.
Latency in myeloid progenitors/monocytes/dendritic cells
Infectious mononucleosis (primary)
Congenital CMV – retinitis, deafness, microcephaly, hepatosplenomegaly in neonate.
Reactivation in immunosuppressed patients – retinitis, colitis, pneumonitis

Question 19

Rhinovirus

Answer 19

Common cold
Aerosolised respiratory secretions and droplets from nose and eyes Sneezing, headache, nasal obstruction and discharge, sore throat, cough, fever

Question 20

Coronaviruses

Answer 20

Aerosolised respiratory secretions and droplets from nose and eyes
Alpha and beta types	
SARS
Covid-19
MERS

Question 21

Influenza

Answer 21

Can spread between species
3 distinct types: A, B and C
Influenza A mutates regularly
Important surface proteins = H and N – mutate regularly
Aerosolised respiratory secretions transmission
Primary influenza – fever, myalgia, then headache, cough, sore throat, nasal discharge
Post-influenza secondary bacterial lung infection - S.pneumoniae, H.influenzae, S.aureus.

Question 22

RSV - Respiratory syncytial virus

Answer 22

Commonest in younger children. Aerosolization of respiratory secretions. Bronchiolitis (affects children < 2 years) – inflammation of bronchioles, causes coughs, wheeze, hypoxia and apnoeas

Question 23

HIV - human immunodeficiency virus

Answer 23

Worldwide - 70% live in sub-Saharan Africa
Virus is present in blood, genital secretions, breast milk
Transmitted vertically, sexually and needlestick
HIV targets helper T lymphocytes (CD4)
2-6 weeks after transmission patients may develop an acute seroconversion illness
Asymptomatic chronic infection -> steady state between virus and immune system (5-15 years)
AIDS= rise in viral load and fall in CD4 count -> vulnerability to opportunistic infections

Question 24

Hepatitis A

Answer 24

Endemic in the developing world – associated with contaminated water: fecal-oral
Nausea, myalgia, fevers, jaundice, right upper quadrant pain
Infection in children is usually asymptomatic, esp. under 5yrs old
50% infected adults are symptomatic
Associated with lower socio-economic groups, returning tourists and men who have sex with men (MSM)

Question 25

Hepatitis B

Answer 25

Vertical transmission – sexual, parenteral
Can cause acute clinical hepatitis
90% children and 50% adults are unaffected
If Hep B becomes chronic -> cirrhosis -> hepatocellular carcinoma. More likely to become chronic if affected when younger.

Question 26

Hepatitis C

Answer 26

Low prevalence in developed countries
In UK – 50% of PWID (people who inject drugs) have evidence of hep C
Transmission by sharing needles, needlestick injuries, transfusion of contaminated products
25% develop acute clinical hepatitis -> from this 85% become chronically infected
Chronic hepatitis -> cirrhosis -> hepatocellular carcinoma

Question 27

Hepatitis E

Answer 27

Endemic in the developing world – associated with contaminated water: fecal-oral
Nausea, myalgia, fevers, jaundice, right upper quadrant pain
95% of cases are asymptomatic (no symptoms)
Fulminant hepatitis with high mortality (25%) in infected pregnant women

Question 28

Norovirus

Answer 28

Short lived immunity. Common. Associated with point-source outbreaks
Ingestion/inhalation of aerosolised vomit particles
Vomiting

Question 29

Rotavirus

Answer 29

Childhood virus, seasonal (peaks in winter), major cause of infant mortality in developing world
Fecal-oral contaminated food/water and aerosolised faeces/vomit
Fever, vomiting and watery diarrhoea

Question 30

Enteroviruses

Answer 30

> 70 serotypes
Includes poliovirus, echoviruses and Coxsackie A and B
Worldwide distribution, mostly in under 15s, 90% are asymptomatic
Enteric route: faeco-oral, contaminated food/water.
Replicate in gut but do not case GI symptoms. From gut -> lymph nodes -> CNS
Fever-rash syndromes in children
Meningitis
Severe disseminated disease in neonate
Poliomyelitis

Question 31

Mumps

Answer 31

Endemic childhood infection.
Virus shed in saliva and respiratory droplets. Very infectious
MMR vaccine exists now
Acute parotitis
Orchitis – affects some males with mumps
Meningitis (can -> meningoencephalitis, sensorineural deafness

Question 32

Measles

Answer 32

Previously endemic in UK, vaccine exists now
Respiratory droplet transmission
Highly infectious
Primary measles
Acute post infectious measles encephalitis
Subacute sclerosing pan-encephalitis

Question 33

Rubella

Answer 33

Rare due to MMR vaccine
Droplet transmission
Primary rubella – mild illness, fever and maculopapular rash. Arthralgia/arthritis.
Congenital rubella – classic triad: bilateral cataracts, sensorineural deafness, cardiac defects

Question 34

Parvovirus B19

Answer 34

Peaks in spring
Respiratory droplet infection
Infects and kills erythrocyte progenitor cells -> causes transient anaemia Erythema infectiosum – fever, coryza, fiery red rash to cheeks, rash on body
Transient aplastic crisis – affects those with high erythrocyte turnover (sickle cell anaemia, thalassemia)
Infection in pregnancy -> small risk of fetal loss or hydrops fetalis (severe fetal anaemia)

Question 35

CJD - Creutzfeldt Jacob disease

Answer 35

Sporadic CJD – very rare
New variant CJD – directly linked to BSE (bovine spongiform encephalopathy), same prion structure, consumption of contaminated beef Progressive ataxia, depression, dementia, death.

Question 36

Ascariasis

Answer 36

Roundworms - nematodes
Life cycle: faecal oral transmission – ingestion of embryonated eggs, larvae enter GI tract and mature in small intestine
Abdominal discomfort or pain. Heavy infections can block the intestines and slow growth in children. Other symptoms such as cough are due to migration of the worms through the body.

Question 37

Schistosomiasis

Answer 37

Flatworms – platyhelminths
Parasitic worm that lives in fresh water in subtropical and tropical regions
Simple indirect lifecycle
Treatment – Praziquantel, check urine and stool microscopy (serology can stay positive 2 months after cure)
Initial incubation = 14-84 days – often asymptomatic
Symptomatic acute infection (rash, fever, headache, myalgia, respiratory symptoms, eosinophilia and hepato-/spleno-megaly)
Chronic infection – bowel symptoms, liver fibrosis, hyperplasia

Question 38

Hydatid disease

Answer 38

Larval stages of cestodes (tapeworms) of Echinococcus genus
Treatment – untreated = high mortality rate by 10 years. Albendazole improves prognosis
Primary infection = always asymptomatic, long latent period, cysts grow very slowly
Hydatid cyst rupture -> develop complications depending on location eg. hepatic – small cysobiliary fistulas, infection, membranous glomerulonephritis

Question 39

Plasmodium spp

Answer 39

Transmission by bite of female Anopheles mosquito
Diagnosis by rapid antigen test
5 species of parasite
Life cycle: sporozoites -> into blood -> human liver stages (schizont) -> human blood stages (trophozoite -> schizont again and repeat or -> gametocyte) -> ingested by mosquito (-> macrogametocyte -> ookinete -> oocyte -> sporozoites)
Malaria
Severe clinical manifestations = parasitaemia, HB

Question 40

Cryptosporidium spp

Answer 40

Sporozoans
Widespread in environment – faecal oral transmission
Direct life cycle
Diagnosis – stool microscopy
Treatment – most resolve spontaneously, immunosuppressed patients can have longer infections
Symptom onset = 2-10 days
Watery diarrhoea, stomach cramps, dehydration, nausea and vomiting, fever, weight loss.

Question 41

Trichomonas vaginalis

Answer 41

Flagellates
Human genital tract (females – vulva, vagina, urethra. Males – mostly urethra)
Direct lifecycle
Diagnosis – detection of motile Trichomonas by light field microscopy
Treatment – Metronidazole
Control – condom/STI screening
Often asymptomatic
Symptoms are more common in women than men, and in older people
Mild irritation to severe inflammation after 5-28 days
Irritation with urination, discharge and unusual smell
Untreated infection can increase risk of STIs

Question 42

Giardia lambia

Answer 42

Flagellates
Faecal oral transmission
Direct life cycle
Diagnosis – at least 3 stool samples over several days. Microscopy with direct fluorescent antibody testing
Treatment – Metronidaole, tinidazole, nitazoxanide…
Symptoms within 1-2 weeks
Diarrhoea, foul smelly greasy stools, stomach cramps, nausea and vomiting, fever, itchy skin
Chronic giardiasis – weight loss, malabsorption of fat soluble vitamins and B12

Question 43

Candida spp

Answer 43

Yeasts
Causes superficial and systemic disease of any organ
Infection usually from patients own colonised mucosa
Avoid oral azole therapy from vaginal thrush in pregnant women (can increase risk of teratology’s), use topical azoles.
Diagnosis of system candidiasis by discovery of candidemia
Colonisation of oral or vaginal mucosa = thrush
Systemic candidiasis – oesophagus, eye, heart valves, endocarditis, urinary tract and peritoneum
Candida in blood culture = candidemia

Question 44

Aspergillus

Answer 44

Mould – produces spores that can be inhaled
Diagnosis – chest imaging
Immunocompromised patients may get invasive aspergillosis – associated with a high mortality, needs rapid aggressive treatment with iv antifungals. Pulmonary or sinus disease
Patients with lung cavity (eg. TB) can get a fungal ball or aspergilloma (often indolent but can cause fatal haemoptysis)
Allergic bronchopulmonary aspergillosis
Chronic pulmonary aspergillosis

Question 45

Dermatophytes

Answer 45

Moulds
Geophilic = from soil, zoophilic = from animals, anthrophillic = from humans
Disease is described by tinea + site of infection
Trichophyton rubrum = common cause of toenail, foot and groin infections
Tinea capitis needs oral antifungal medication – topicals are insufficient Causes diseases of skin, hair and nails
Itching, fissuring, flaking of skin
Uni- or bi- lateral

Question 46

Malassezia

Answer 46

Yeasts
Commensals on everyone’s skin
Response is caused by changes with how they interact with skin Pityriasis versicolor with hypo or hyperpigmented patches of skin.