UKMLA: Infectious Disease

Gram-Positive Bacteria

Bacteria with a thick peptidoglycan cell wall that stains violet with crystal violet stain

Gram-Negative Bacteria

Bacteria lacking a thick peptidoglycan cell wall, do not retain the crystal violet stain, and instead stain red or pink with a counterstain such as safranin.

Atypical Bacteria

Bacteria that cannot be stained or cultured using standard techniques, including organisms causing atypical pneumonia such as Mycoplasma pneumoniae and Legionella pneumophila.

Beta-Lactam Antibiotics

Antibiotics that inhibit bacterial cell wall synthesis via a beta-lactam ring; examples include penicillins, cephalosporins, and carbapenems.

Non-Beta-Lactam Cell Wall Inhibitors

Antibiotics such as vancomycin and teicoplanin that inhibit bacterial cell wall synthesis without containing a beta-lactam ring

Metronidazole Mechanism Of Action

Inhibits bacterial nucleic acid synthesis, disrupting DNA replication and leading to bacterial death.

Ribosome-Targeting Antibiotics

• Macrolides→ -mycin

• Tetracyclines→ doxycycline

• Gentamycin

Folic Acid Pathway In Bacteria

• Para-aminobenzoic acid (PABA) converted to dihydrofolic acid (DHFA)→ tetrahydrofolic acid (THFA)→ folic acid

• Blocked by sulfamethoxazole

Trimethoprim Mechanism Of Action

Inhibits the conversion of dihydrofolic acid (DHFA) to tetrahydrofolic acid (THFA)

Gram Stain Procedure

1. Apply crystal violet stain – stains gram-positive bacteria violet.

2. Apply counterstain (e.g., safranin) – stains gram-negative bacteria red/pink.

Gram-Positive Cocci

• Staphylococcus

• Streptococcus

• Enterococcus

Gram-Positive Rods

• Corynebacteria

• Mycobacteria

• Listeria

• Bacillus

• Nocardia

Gram-Positive Anaerobes: CLAP Mneumonic

• Clostridium

• Lactobacillus

• Actinomyces

• Propionibacterium

Gram Negative Bacteria

• Neisseria meningitidis

• Neisseria gonorrhoeae

• Haemophilus influenzae

• Escherichia coli

• Klebsiella

• Pseudomonas aeruginosa

• Moraxella catarrhalis

MRSA

Staphylococcus aureus that has developed resistance to beta-lactam antibiotics, including penicillins, cephalosporins, and carbapenems

MRSA Eradication Measures

Combination of chlorhexidine body washes and antibacterial nasal creams to eliminate colonisation

Extended-Spectrum Beta-Lactamase (ESBL) Bacteria

Bacteria, usually E. coli or Klebsiella, that produce beta-lactamase enzymes destroying the beta-lactam ring, causing resistance to many antibiotics. Commonly cause UTIs, pneumonia, and septicaemia.

Management Of Extended-Spectrum Beta-Lactamase (ESBL) Bacteria

Nitrofurantoin or phosphomycin

Nitrofurantoin Mechanism Of Action

exclusively for lower urinary tract infections→ bactericidal

Amoxicillin

Used for:

• Streptococci

• Listeria

• Enterococci

Co-Amoxiclav

Used for:

• Staphylococci

• Haemophilus

• E.coli

Cellulitis

When a patient presents with cellulitis, look for a breach in the skin barrier and a point of entry for the bacteria. This may be due to skin trauma, eczema, fungal nail infections or ulcers.

Presentation Of Cellulitis

Skin changes in cellulitis include:

• Erythema (red discolouration)

• Warm or hot to touch

• Tense

• Thickened

• Oedematous

• Bullae (fluid-filled blisters)

• A golden-yellow crust indicates a Staphylococcus aureusinfection

Eron Classification For Cellulitis

The Eron classification assesses the severity of cellulitis:

• Class 1 – no systemic toxicity or comorbidity

• Class 2 – systemic toxicity or comorbidity

• Class 3 – significant systemic toxicity or significant comorbidity

• Class 4 – sepsis or life-threatening infection

Management Of Cellulitis

Class 3 and 4 cellulitis requires admission for intravenous antibiotics. Admission is also considered for frail, very young or immunocompromised patients and those with facial, periorbital or orbital cellulitis.

Flucloxacillin is the usual first-line antibiotic for cellulitis, either oral or intravenous.

Management Of Cellulitis Near Eyes Or Nose

Co-amoxiclav

Clostridium Difficile

• Gram positive, rod-shaped anaerobic bacteria

• Associated with repeated antibiotic or PPI use

• Faecal transmission

Drugs Associated With Causing C.Difficile

Antibiotics and PPI’s:

• Clindamycin

• Ciprofloxacin (and other fluoroquinolones)

• Cephalosporins

• Carbapenems (e.g., meropenem)

Presentation Of C.Difficile

Colonisation is usually asymptomatic.

Infection presents with diarrhoea, nausea and abdominal pain.

Severe infection with colitis can present with:

• Dehydration

• Systemic symptoms (e.g., fever, tachycardia and hypotension)

Diagnosis Of C.Difficile

Diagnosis is based on stool samples. Stools can be tested for:

• C. difficile antigen (specifically glutamate dehydrogenase)

• A and B toxins (by PCR or enzyme immunoassay)

 

The antigen test shows whether C. difficile is present but not whether it is producing toxins. The antigen is the initial screening test and is followed up with tests for toxins if C. difficile is identified.

Management Of C.Difficile

Management is with supportive care and oral antibiotics. The options are:

• Oral vancomycin (first-line)

• Oral fidaxomicin (second-line)

 

Patients need to be isolated until 48 hours after the last episode of diarrhoea. There is a high recurrence rate.

Faecal microbiota transplantation is an option for recurrent cases. The stool microbiome from a donor is transferred to the patient via capsules, colonoscopy or enema.

Complications Of C.Difficile

• Psuedomembranous colitis→ inflammation in large intestine with yellow/white plaques

• Toxic megacolon→ severe inflammation. High risk of bowel rupture.

Encephalitis

The most common viral cause is herpes simplex virus (HSV). In children the most common cause is herpes simple type 1 (HSV-1) from cold sores. In neonates it is herpes simplex type 2 (HSV-2) from genital herpes, contracted during birth.

Presentation Of Encephalitis

• Altered consciousness

• Altered cognition

• Unusual behaviour

• Acute onset of focal neurological symptoms

• Acute onset of focal seizures

• Fever

 

Diagnosis Of Encephalitis

• Lumbar puncture, sending cerebrospinal fluid for viral PCRtesting

• CT scan if a lumbar puncture is contraindicated

• MRI scan after the lumbar puncture to visualise the brain in detail

• EEG recording can be helpful in mild or ambiguous symptoms but is not always routinely required

• Swabs of other areas can help establish the causative organism, such as throat and vesicle swabs

• HIV testing is recommended in all patients with encephalitis

Contraindications to a lumbar puncture include a GCS below 9, haemodynamically unstable, active seizures or post-ictal.

Management Of Encephalitis

• Aciclovir treats herpes simplex virus (HSV) and varicella zoster virus (VZV)

• Ganciclovir treat cytomegalovirus (CMV)

Repeat lumbar puncture is usually performed to ensure successful treatment prior to stopping antivirals

Complications Of Encephalitis

• Lasting fatigue and prolonged recovery

• Change in personality or mood

• Changes to memory and cognition

• Learning disability

• Headaches

• Chronic pain

• Movement disorders

• Sensory disturbance

• Seizures

• Hormonal imbalance

 

Otitis Media

Otitis media refers to infection in the middle ear

Rhinitis

Rhinitis refers to inflammation of the nasal mucosa

Common Cause Of Ear Nose And Throat Infections

Most ear, nose and throat infections are viral and resolve spontaneously within 1–3 weeks

Indications For Antibiotics In Ent Infections

Antibiotics are reserved for immunocompromised patients, those with significant comorbidities, severe infections, or infections that fail to resolve.

Backup Prescription

A backup prescription allows patients to collect antibiotics if symptoms do not improve or worsen after 3 days

Common Bacterial Cause Of Tonsillitis

Group A Streptococcus (GAS), primarily Streptococcus pyogenes.

Common Bacterial Causes Of Otitis Media Sinusitis And Tonsillitis

Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, and Staphylococcus aureus.

A scoring system giving one point for each of the following: fever >38°C, tonsillar exudates, absence of cough, and tender anterior cervical lymph nodes. A score of 3 or more indicates 40–60% probability of bacterial infection and warrants antibiotics.

Feverpain Score For Bacterial Tonsillitis

A scoring system with one point each for: fever in previous 24 hours, purulence on tonsils, attended within 3 days of onset, inflamed tonsils, and no cough or coryza. Scores of 2–3 indicate 34–40% probability; 4–5 indicate 62–65% probability of bacterial tonsillitis.

First-Line Antibiotic For Bacterial Tonsillitis

Penicillin V (phenoxymethylpenicillin) for 10 days, effective against Streptococcus pyogenes.

Alternative Antibiotic For Tonsillitis In Penicillin Allergy

Clarithromycin

Complications Of Tonsillitis

Peritonsillar abscess (quinsy), otitis media, scarlet fever, rheumatic fever, post-streptococcal glomerulonephritis, and post-streptococcal reactive arthritis

Presentation Of Otitis Media

Reduced hearing and ear pain with a bulging red tympanic membrane on otoscopy. Perforation may cause ear discharge.

Natural Course Of Otitis Media

Usually resolves within 3–7 days without antibiotics. Admission may be required if systemically unwell.

First-Line Antibiotic For Otitis Media

Amoxicillin for 5–7 days.

Second-Line Antibiotic For Otitis Media

Co-amoxiclav if infection is not responding to amoxicillin.

Duration Of Sinusitis

Acute sinusitis typically lasts 2–3 weeks and resolves without treatment.

Management Of Sinusitis Not Improving After 10 Days

High-dose steroid nasal spray for 14 days (e.g., mometasone 200 mcg twice daily) or a backup antibiotic prescription (phenoxymethylpenicillin first-line)

Management Of Chronic Sinusitis

Saline nasal irrigation, steroid nasal sprays or drops (e.g., mometasone or fluticasone), and functional endoscopic sinus surgery (FESS)

Acute Gastritis

Stomach inflammation and epigastric discomfort, nausea and vomiting

Enteritis

Inflammation of the intestines, abdominal pain and diarrhoea

E Coli

E. coli 0157 produces the Shiga toxin. The Shiga toxin causes abdominal cramps, bloody diarrhoea and vomiting. It also destroys blood cells, leading to haemolytic uraemic syndrome (HUS)

Use Of Antibiotics With E.Coli Infection

The use of antibiotics increases the risk of haemolytic uraemic syndrome. Therefore, antibiotics should be avoided if E. coligastroenteritis is a possibility.

Campylobacter Jejuni

• Campylobacter is a common cause of travellers’ diarrhoea

• Most common cause of gastroenteritis

• Gram-negative, curved or spiral bacteria

• Spread via raw poultry, untreated water, raw milk

Symptoms Of Campylobacter Jejuni

Incubation is usually 2 to 5 days. Symptoms resolve after 3 to 6 days. Symptoms are:

• Abdominal cramps

• Diarrhoea often with blood

• Vomiting

• Fever

Management Of Campylobacter Jejuni

Clarithromycin is often first-line. Azithromycin and ciprofloxacin are alternative options.

Shigella

• Spread via faeces (person or contamination)

• 1-2 days incubation period

• Symptoms resolve within 1 week: bloody diarrhoea, cramps and fever

• Manage via azithromycin

Salmonella

• Raw eggs, raw poultry or animal-faeces contaminated food

• 12 hours to 3 days incubation period Symptoms resolve d

• Symptoms: watery diarrhoea, vomiting, pain

Bacillus Cereus

• Gram positive rod

• Contaminated cooked food

• Cerulide toxin→ cramping and vomitting within 5 hours of ingestion

• The typical course is vomiting within 5 hours, diarrhoea after 8 hours and resolution within 24 hours.

Yersinia Enterocolitica

• Gram-negative bacillus

• Raw or undercooked pork

• Typically affects children

• 4-7 days incubation period

• Symptoms over 3 weeks: right-sided abdominal pain

Staphylococcus Enterotoxins

• Eggs, meat, dairy

• Symptoms of diarrhoea, vomiting, abdominal cramps and fever. These symptoms start within hours of ingestion and settle within 12 to 24 hours

Giardiasis

• Parasite in small intestine of animals→ cysts in faeces contaminate food or water

• Manage via tinidazole or metronidazole

Oral Rehydration Solution

These contain glucose, potassium and sodium

Anti-diarrhoeal Drug

Loperamide

Anti-emetic Drug

Metoclopramide

Hepatitis B

DNA virus→ sharing toothbrushes, sex, blood, minor cuts, vertical transmission

Hepatitis B In Children

The risk of developing chronic hepatitis Bafter exposure is:

• 90% for neonates

• 30% for children under 5

• Under 10% for adolescents

Children To Test For Hepatitis B

• Children of hepatitis B positive mums (screen at 12 months of age or any time after that)

• Migrants from endemic areas

• Close contacts of patients with hepatitis B

Hepatitis B Positive Mothers

reduce the risk of the baby contracting hepatitis B, at birth (within 24 hours) neonates with hepatitis B positive mothers should be given both:

• Hepatitis B vaccine

• Hepatitis B immunoglobulin infusion

Infants are given an additional hepatitis B vaccine at 1 and 12 months of age. They will also receive the hepatitis B vaccine as part of the normal 6 in 1 vaccine given to all infants aged 8, 12 and 16 weeks. They are tested for the HBsAg at 1 year to see if they have contracted hepatitis B.

 

Complications Of Hepatitis B

Where there is evidence of hepatitis or cirrhosis, treatment with antiviral medications may be considered.

Hepatitis B Screening

When screening for hepatitis B, test HBcAb (for previous infection) and HBsAg (for active infection). If these are positive do further testing for HBeAg and viral load (HBV DNA).

HBsAb demonstrates an immune response to HBsAg. The HBsAg is given in the vaccine, so having a positive HBsAb may simply indicate they have been vaccinated and created an immune response to the vaccine.HBV DNA).

Hepatitis C

• RNA virus

• NO vaccine available

• Curable in adults via direct acting antiviral medications

Hepatitis C Disease Course

In adults:

• 1 in 4 fight off the virus and make a full recovery

• 3 in 4 develop chronic hepatitis C

Complications:

• Liver cirrhosis and associated complications of cirrhosis

• Hepatocellular carcinoma

Investigations For Hepatitis C

• Hepatitis C antibody is the screening test

• Hepatitis C RNA testing is used to confirm the diagnosis of hepatitis C, calculate viral load and identify the genotype

Hepatitis C And Breastfeeding/Pregnancy

Babies to hepatitis C positive mothers are tested at 18 months of age using the hepatitis C antibody test. Breastfeeding has not been found to spread hepatitis C, so mothers are free to breastfeed their babies. If nipples become cracked or bleed breastfeeding should temporarily stop whilst they heal.

Management Of Hepatitis C In Children

• Medical treatment may be considered in children over 3 years. Treatment in childhood involves pegylated interferon and ribavirin

• Treatment is typically delayed until adulthood unless the child is significantly affected, because children are usually asymptomatic and newly available treatment for adults is highly effective.

Infectious Mononucleosis

Infectious mononucleosis (IM) is a condition caused by infection with the Epstein Barr virus (EBV). It is commonly known as the “kissing disease”, “glandular fever” or “mono”. This virus is found in the saliva of infected individuals.

Symptoms Of Infectious Mononucleosis

Typical symptoms are fever, sore throat, fatigue, splenomegaly

May cause itchy maculopapular rash in response to amoxicillin

Monospot Test

• Monospot test: this introduces the patient’s blood to red blood cells from horses. Heterophile antibodies (if present) will react to the horse red blood cells and give a positive result.

Paul-Bunnell Test

• Paul-Bunnell test: this is similar to the monospot test but uses red blood cells from sheep.

Specific Epstein-Barr Virus Antibody Tests

It is possible to test for specific EBV antibodies. These antibodies target something called viral capsid antigen (VCA):

• The IgM antibody rises early and suggests acute infection

• The IgG antibody persists after the condition and suggests immunity

Management And Prognosis Of Infectious Mononucleosis

Infectious mononucleosis is usually self limiting. The acute illness lasts around 2 – 3 weeks, however it can leave the patient with fatigue for several months once the infection is cleared.

Patients are advised to avoid alcohol, as EBV impacts the ability of the liver to process the alcohol. Patients are advised to avoid contact sports due to the risk of splenic rupture. Emergency surgery is usually required if splenic rupture occurs.

Complications Of Epstein-Barr Virus

• Splenic rupture

• Glomerulonephritis

• Haemolytic anaemia

• Thrombocytopenia

• Chronic fatigue

EBV infection is associated with certain cancers, notable Burkitt’s lymphoma.

 

Influenza

• RNA virus

• A,B,C → affects humans

• D→ affects cattle

Influenza Vaccination

The flu vaccine is free on the NHS to people at higher risk of developing flu or flu-related complications:

• Aged 65 and over

• Young children

• Pregnant women

• Chronic health conditions, such as asthma, COPD, heart failure and diabetes

• Healthcare workers and carers

Presentation Of Influenza

The delay between exposure and symptoms is usually around 2 days. Typical presenting features include:

• Fever

• Lethargy and fatigue

• Anorexia (loss of appetite)

• Muscle and joint aches

• Headache

• Dry cough

• Sore throat

• Coryzal symptoms

Management Of Influenza

• Oral oseltamivir (twice daily for 5 days)

• Inhaled zanamivir (twice daily for 5 days)

Treatment needs to be started within 48 hours of the onset of symptoms to be effective.

Malaria

• Protozoan parasites→ plasmodium falciparum

• Bite of female anopheles mosquitoes