Infections eBook Flashcards
Infections are caused by the following groups of organisms:
Viruses
Bacteria
Eukaryotes – protozoa, fungi and parasitic worms
Infectious disease accounts for around 25% of deaths worldwide.
what causes an infection
Organism + Host = Infection
organisms: Viruses Fungi Bacteria Protozoa
host (human): Natural defences against infection: • Physical • Lysozymes • pH • Phagocytosis • Complement & plasma proteins
There are a number of ways that the body protects us from infection.
These include:
Physical defences against infections include skin barriers, mucus & cilia that capture organisms and remove them and urinary flushing. Skin diseases e.g. eczema/psoriasis can allow colonization and invasion by pathogens due to a breakdown in the physical defence barrier.
Lysozyme in tears degrades gram positive bacterial peptidoglycan.
Stomach acid protects from ingested pathogens and acid suppression increases the risk of intestinal infection.
Phagocytes – neutrophils & macrophages ingest particles including bacteria, viruses and fungi
Complement & other plasma proteins – complement cascade is activated by antigenantibody
binding or by direct interaction with bacterial cell wall components. This attracts phagocytes to the site of the infection
local symptoms of infection
purulent sputum production
local erythema
presence of pus
dysuria
Bacteria
Bacteria are prokaryotic cells that exist in various shapes including spheres (cocci), curves, spirals and rods (bacilli). These form the basis for primary classification.
They are also divided broadly into two main groups according to their Gram stain reaction;
Gram-positive or Gram-negative (do not retain Gram stain). Gram-positive cell walls have a thick peptidoglycan layer and a cell membrane, whereas Gram-negative cell walls have three layers: an inner and outer membrane and a thin peptidoglycan layer.
Bacteria undertake processes of growth, energy generation and reproduction independently of other cells and can grow in a wide variety of environments e.g. hot sulphur springs, freezers, low or high pH.
They are also classified as aerobic or anaerobic which relate to whether they grow in the presence or absence of oxygen.
Antibacterials can be classified according to their site of action:
- Cell wall active antibacterials
beta lactams, glycopeptides, carbapenems - Protein synthesis inhibitors
aminoglycosides, macrolides, tetracyclines, clindamycin, fusidic acid, linezolid, - Nucleic acid synthesis inhibitors
quinolones, nitrofurantoin, metronidazole, trimethoprim, co-trimoxazole, rifampicin
Antibacterial agents are also described as being either:
Bactericidal agents – kill the bacteria.
Bacteriostatic agents – inhibit proliferation of the bacteria but do not kill them.
Choice of Antibacterial Agent
This depends on many factors and includes:
- Spectrum of activity depending on most likely pathogens as culture & sensitivities can take time.
- Local policies and guidelines.
- Resistance patterns.
- Pharmacokinetics and the ability of the antibacterial to reach site of action.
- Patient factors including renal function, hepatic function, age, co-morbidities, allergies, drug interactions, pregnancy, breastfeeding or immunosuppressed.
- Combination therapy – broad spectrum & ↓ resistance.
- Route of antibacterial agent
Skin and Soft Tissue Infection
The majority of these infections are caused by Gram-positive Staphylococcus aureus and Streptococcus pyogenes. Most of these infections are due to bacteria on the skin surface penetrating the dermis or subcutaneous
tissues.
Impetigo
This is a superficial skin infection usually seen in children and young adults. It is spread by direct contact. Lesions usually occur on the face and extremities and vesicular-purulent bullous or popular in appearance. Yellow or brown crusting is characteristic and secondary cellulitis can occur.
Treatment
Localised disease is treated with topical fusidic acid and mupirocin (if MRSA). More extensive disease is treated with oral antibiotics for 7-10 days (usually flucloxacillin if Staphylococcus and penicillin V for Streptococcus)
Cellulitis
Cellulitis is a common cause of hospital admission in the UK and is an infection in the deeper dermis or subcutaneous fat.
Symptoms include heat, erythema, induration and localised tenderness of the skin area.
Patients often are generally unwell and with pyrexia.
It is usually caused by Streptococcus or Staphylococcus but in the immunocompromised or diabetic patients Gram-negative or anaerobic bacteria should also be suspected. There is usually evidence of an entry port in cellulitis so a careful history should be taken from the patient.
Necrotising skin and soft tissue infections
This is a severe and life-threatening infection with a systemic inflammatory response, involvement of deep tissues and associated tissue destruction.
Symptoms include a combination of severe, constant pain, blistering and bruising, oedema, gas in the tissues (gas gangrene), systemic inflammatory response and multi-organ failure.
Predominately caused by aerobic gram-positive cocci (Streptococcus pyogenes and Staphylococcus aureus).
Respiratory Tract Infections
These are divided into:
Upper respiratory tract infections o Common cold o Influenza o Sinusitis o Pharyngitis o Otitis media
usually self-limiting and may be caused by viruses
Lower respiratory tract infections o Pneumonia o Tuberculosis o Exacerbation of COPD o Bronchitis
Acute otitis media (AOM)
AOM is an infection of the middle ear, characterized by the presence of middle ear effusion associated with the acute onset of symptoms and signs of middle ear inflammation. The most common bacterial pathogens associated with AOM are Streptococcus pneumoniae,
Haemophilus influenzae, and Moraxella catarrhalis. AOM may also be caused by virus, most commonly respiratory syncytial virus and rhinovirus.
Treatment
It is a common self-limiting disease in children and 80% of cases will resolve in 3 days without any treatment. Complications are rare and antibiotics should not be prescribed routinely to these patients.
Antibiotics may be beneficial in the following sub-groups of patients.
For example, children:
– Under two years with bilateral infection or
– With discharge from the ear or
– Who are systemically unwell (e.g. fever or vomiting) or
– With recurrent infections.
Amoxicillin or clarithromycin are the usual first line antibiotics for AOM.
Sinusitis
Acute sinusitis is a common infection of the paranasal sinuses, with inflammation of the nasal and sinus mucosa. It is usually caused by viral infection but may be complicated by a secondary bacterial infection.
Symptoms of acute sinusitis include nasal discharge, nasal congestion, headache, earache, facial pain, maxillary tooth discomfort and fever.
Treatment
It is usually self-limiting so treatment with antibiotics is not necessary, unless symptoms including purulent discharge have persisted for 7-10 days, or the patient is
immunocompromised. If antibiotics are necessary amoxicillin, doxycycline or clarithromycin are
recommended first-line. Clarithromycin may be substituted for erythromycin, but this is less effective against Haemophilus influenzae, which is the cause of sinusitis in around a fifth of cases.
Acute Bronchitis
In previously healthy subjects this is often viral but can be followed by infections with organisms such as Streptococcus pneumoniae and Haemophilus influenzae. This is more common in cigarette smokers or those with COPD.
Symptoms include an irritating, non-productive cough with discomfort behind the sternum. This may also be associated with tightness of the chest, wheezing and shortness of breath. The cough usually becomes productive where the sputum turns yellow or green and there is mild pyrexia.
The symptoms usually resolve spontaneously in 3-4 days in healthy patients.
Treatment
Not always necessary but may be treated with amoxicillin or a tetracycline.
Pneumonia
Pneumonia is defined as an infection of the lung parenchyma (the functional tissue of the lungs). The
infection manifests itself in the alveoli, as this is the main air-exchange surface for oxygen and carbon dioxide pneumonia can be sever and life threatening. Pneumonia can be divided into two broad types:
Community Acquired and Hospital acquired.
Community acquired pneumonia (CAP): symptoms, signs and severity – adult
Symptoms and signs:
Dyspnoea, cough, malaise, fever, sweats, aches and pains, pleural pain, tachypnoea, confusion
Severity:
Clinical judgement is essential in disease severity assessment, consider stability of co-morbid illness and
patient’s social circumstances.
Investigations – adult
Investigations carried out are dependent on whether patient is treated in community or hospital and on
the severity of the pneumonia. Clinical judgement is used
Severity assessment in the community – adult
The need for hospital referral should be assessed using clinical judgment and CRB-65 scoring system
CRB65 score for mortality risk assessment in primary care
CRB65 score is calculated by giving 1 point for each of the following prognostic features:
confusion (abbreviated Mental Test score 8 or less, or new disorientation in person, place or time)
raised respiratory rate (30 breaths per minute or more)
low blood pressure (diastolic 60 mmHg or less, or systolic less than 90 mmHg)
age 65 years or more.
Patients are stratified for risk of death as follows:
0: low risk (less than 1% mortality risk)
1 or 2: intermediate risk (1-10% mortality risk)
3 or 4: high risk (more than 10% mortality risk).
pneumonia General Management – adult in the community
Assessment of severity of pneumonia
Advise rest
Drink plenty of fluids
Stop smoking
Simple analgesia (e.g. paracetamol)
Assess for hospital referral
Pulse oximetry
Review again after 48 hours or earlier if clinically indicated include disease severity assessment
Consider hospital admission or chest radiography in those who fail to improve after 48 hours
Severity assessment – adults admitted to hospital
The CURB-65 score is used to determine the severity and subsequent management of CAP in patients
CURB65 score for mortality risk assessment in hospital
CURB65 score is calculated by giving 1 point for each of the following prognostic features:
confusion (abbreviated Mental Test score 8 or less, or new disorientation in person, place or time)
raised blood urea nitrogen (over 7 mmol/litre)
raised respiratory rate (30 breaths per minute or more)
low blood pressure (diastolic 60 mmHg or less, or systolic less than 90 mmHg)
age 65 years or more.
Patients are stratified for risk of death as follows:
0 or 1: low risk (less than 3% mortality risk)
2: intermediate risk (3-15% mortality risk)
3 to 5: high risk (more than 15% mortality risk).
pneumonia General investigations – adult patient admitted to hospital
Oxygen saturations / arterial blood gases in accordance with the BTS guideline for Emergency Oxygen Use in Adult Patients) Chest Radiograph U and Es to inform severity assessment CRP FBC LFTs
pneumonia General management – hospital
Appropriate oxygen therapy
Assess for volume depletion – may require IV fluids
Consider prophylaxis of venous thromboembolism
Mobilisation – see BTS guidance
Nutritional support in prolonged illness
Advice and treatment regarding expectoration if sputum is present
pneumonia Monitoring in hospital
Monitor - temperature, respiratory rate, pulse, blood pressure, mental status, oxygen saturation,
inspired oxygen concentration (at least twice daily, consider more frequently)
If not progressing satisfactorily after 3 days of treatment – repeat CRP and chest radiograph
Review within 24 hours of planned discharge
pneumonia CAP – hospitalised patients
Patients admitted to hospital may need critical care management. All patients will need to have followup
arrangements made prior to discharge from hospital.
pneumonia Microbiological investigations – adult
These are dependent on severity of CAP, treatment in hospital or community and other factors
Microbiological tests should be performed on all patients with moderate and high severity CAP – the extent of investigation is guided by severity of CAP Diagnosis of low severity CAP - the extent of microbiological investigations should be guided by prior antibiotic therapy epidemiological factors and clinical factors (age, co-morbid illness, and severity indicators).
Examples of Microbiological investigations – adult
Sputum cultures and sensitivities (before antibiotic therapy is commenced)
Sputum Gram stain
Blood cultures (preferably before antibiotic therapy is commenced)
Urine antigen tests
PCR
Serology
Antibiotic management – adult
Consider local issues e.g. resistance patterns, C. difficile associated diarrhoea
Empirical therapy – change according to cultures and sensitivities
Switch from IV to oral antibiotic therapy appropriately.
Community Acquired Pneumonia – adult: other considerations
Complications and failure to improve
Prevention and vaccination: pneumococcal vaccination and annual influenza vaccination
Advise smoking cessation in those patients who smoke
Hospital acquired pneumonia (HAP)
HAP is a respiratory infection developing more than 48 hours after hospital admission. The causative organism is unlikely to be the same as those that commonly cause CAP. The choice of empirical antibiotic treatment is in accordance with the knowledge of local sensitivity and resistance patterns and individual patient’s circumstances.
Patients with hospital-acquired pneumonia should be offered antibiotic therapy as soon as possible after
diagnosis (certainly within 4 hours). A 5- to 10-day course of antibiotic therapy should be considered
viruses contain either
dna or rna, not both
They have a central nucleic acid core surrounded by a protein coat. Some viruses are surrounded by a lipid envelope derived from the host cell or nuclear membranes.
Viruses are intracellular parasites as they are metabolically inert. They use the host cell for synthesis of viral proteins & nucleic acid.
Many viral infections are self-limiting in immunocompetent individuals and do not require treatment other than symptomatic support.
Antibiotics have
no efficacy against viral infections.
Influenza
Influenza is an enveloped orthomyxovirus containing a negative single-stranded RNA genome divided into eight segments. The virus expresses seven proteins, three of which are responsible for RNA transcription.
influenza symptoms
Incubation period is 1 – 4 days, with patients being infectious for a day preceding and the first 3 days of symptoms. Headache, myalgia, fever and cough last for 3 – 4 days. A persistent dry cough can last for several weeks.
Complications include bacterial pneumonia especially in elderly and patients with cardiovascular and pulmonary disease. The severity of the illness reflects pre-existing host immunity and the causative viral strain
influenza Treatment
Influenza should be treated symptomatically (e.g. antipyretics, rest and fluids). If a secondary bacterial infection develops, appropriate antibiotics should be prescribed.
The neuraminidase inhibitors zanamivir (Relenza®) and oseltamivir (Tamiflu®) shorten the duration of symptoms and should be used in accordance with NICE guidelines or, in the case of pandemic, national and local guidelines.
Neuraminidase inhibitors interfere with the release of virus particles from the host cell which prevents the infection of new host cells and the spread of the respiratory disease. As replication of the influenza virus in the respiratory tract peaks between 24 and 72 hours after the onset of the illness neuraminidase inhibitors must be administered as early as possible.
influenza prevention
Vaccination is the first-line intervention to prevent influenza and all eligible people should receive vaccination. Vaccination provides approximately 70% protection against influenza. Due to viral mutation and short duration of protection a new vaccine needs to be produced and received annually.
Pharmacists often administer influenza vaccinations as part of an enhanced service in conjunction with local clinical commissioning groups or as part of a private PGD. More information can be found in “The Green Book”, the government guide to vaccine preventable diseases.
Measles and how it is transmitted
Measles is a vaccine preventable disease for which there is a national immunisation programme in the UK. It is caused by a paramyxovirus and spread by respiratory contact.
In 2011, there were 158 000 measles deaths globally, mostly children under 5 years. More than 95% of measles deaths occur in low-income countries with weak health infrastructures.
Measles vaccination resulted in a 71% drop in measles deaths between 2000 and 2011 worldwide.
It is transmitted by the aerosol route. The period of infectivity is from 4 days before until 2 days after the onset of the rash, with an incubation period of 9 to 12 days. Mortality is rare in healthy children but the mortality rate is highest in <2yrs
Measles symptoms
Infection begins with a 2 – 4 day cold like illness, when small white papules (Koplik’s spots) are found on the buccal mucosa. This is a diagnostic sign for measles.
A maculopapular rash then develops initially on the face then spreads rapidly to involve the rest of the body. The rash fades after a week leaving a brownish discolouration.
Secondary pneumonia, otitis media, pneumonitis, myocarditis, pericarditis and encephalitis are
complications associated with measles infection.
Herpes Viruses
The herpes viruses are a family of enveloped DNA viruses that characteristically cause latent infections. After primary infection the viral DNA lies dormant in various tissues and may be reactivated. They include:
Herpes simplex virus (HSV, type 1 and2)
Varicella-zoster virus (VZV)
Cytomegalovirus (CMV)
Epstein-Barr virus (EBV)
Human herpes viruses (HHV), types 6 – 8
Herpes simplex virus (HSV)
Reactivation may be triggered by physical factors (e.g. infection, sunlight) or psychological stress.
HSV-1 is the major cause of herpetic stomatitis, herpes labialis (cold sore), keratoconjunctivitis and encephalitis.
HSV-2 causes genital herpes (it may also be caused by HSV-1) and may also be responsible for systemic infection in the immunocompromised host.
These divisions are not rigid as e.g. HSV-2 can also cause oropharyngeal disease HSV-1 is often asymptomatic, but young children commonly develop fever, vesicular
gingivostomatitis and lymphadenopathy. Adults may exhibit pharyngitis and tonsillitis. It is highly contagious and transmitted primarily via saliva. Primary eye infection produces severe keratoconjunctivitis and recurrent infection may result in corneal scarring.
7 development stages of recurrent herpes labialis:
Phase Duration Prodromal 1 day Erythema 1-2 days Papule 1-2 days Vesicle 1-2 days Ulcer 1-3 days Crust 4-14 days Skin re-epithelisation 4-14 days
HSV-2 infections cause painful genital ulceration that can be severe with symptoms lasting up to 3 weeks. Recurrent infections are milder and virus shedding is short-lived, but infection can be transmitted to sexual partners during this time.
Herpes simplex virus (HSV) - Treatment
Topical, oral and intravenous antivirals are available for the treatment of HSV infections. The preparation will depend on the symptoms. Encephalitis is treated with intravenous aciclovir.
Varicella Zoster Virus
Varicella Zoster Virus (VZV) has only one serological type and causes the acute primary infection known as chickenpox or varicella. After primary infection the virus lays dormant in the sensory nervous system to re-emerge as shingles. It is also known as Herpes zoster.
Chickenpox
Chickenpox is most common in children aged 4-10. It is highly infectious and the disease is spread primarily by respiratory droplets although the vesicular fluid is also infectious.
Chickenpox symptoms
The first symptoms are usually a low-grade fever, malaise and sometimes mild influenza like symptoms.
A rash usually develops up to six days later. The rash commonly starts behind the ears, face or trunk and then spreads further. The spots (erythematous, maculopapular) start then turn into vesicles before becoming pustules and crusting over and healing. Vesicular fluid contains large numbers of VZV so when the vesicle ruptures, VZV is transmitted by airborne spread, direct contact with vesicle fluid or indirect contact with infected clothes, towels or bedding.
Individuals are infectious from about 48 hours before and until 5-6 days after the appearance of the first spots and the incubation period is usually 14-21 days.
Chickenpox Treatment
Symptomatic management is all that is usually required in immunocompetent individuals and otherwise healthy children between the ages of 1 month and 12 years.
Antipyretics for fever and flu-like symptoms.
Oral antihistamines and topical preparations (e.g. crotamiton, calamine) can be used for itching.
For immunocompetent adults and adolescents (aged 14 years or older), aciclovir is considered if they present within 24 hours of rash onset, particularly for people with severe chickenpox or those at risk of complications, such as smokers or people using corticosteroids. Normally oral treatment will suffice at a dose of 800mg five times daily for seven days.
Immunocompromised individuals will normally require intravenous therapy at a dose of 10mg/kg TDS for five days.
If serious complications (such as pneumonia, encephalitis, or dehydration) are suspected, admit to hospital for parenteral antiviral treatment.
Shingles
Shingles results from reactivation of latent VZV. Virus reactivation may be caused by age, disease, physical or emotional stress, fatigue or in the immunocompromised.
