Erysipelas is a rare infection of the skin and subcutaneous tissues observed frequently in elderly patients. It is characterized by an acute spreading skin lesion that is intensely erythematous with a plainly demarcated but irregular edge. It is most commonly caused by Streptococcus pyogenes or Group A Streptococcus (GAS).GAS are susceptible to penicillin, which remains the drug of choice for treatment. For patients allergic to penicillin, erythromycin can be used.S. pyogenes colonizes the throat and skin on humans, making these sites the primary sources of transmission. Infections resulting from S. pyogenes include pharyngitis, scarlet fever, skin or pyodermal infections, and other septic infections. In addition, the sequelae rheumatic fever and acute glomerulonephritis can occur as a result of infection with S. pyogenes.Agammaglobulinemia is mostly associated with S. pneumoniae.The M protein is attached to the peptidoglycan of the cell wall and extends tothe cell surface. The M protein is essential for virulence. The polysaccharide capsule is characteristic of S. pneumoniae.

Epstein-Barr virus causes infectious mononucleosis which is a clinical entity characterized by sore throat, cervical lymph node enlargement, fatigue and fever. It is accompanied by atypical large peripheral blood lymphocytes. These atypical lymphocytes, also known as Downey cells, are actually activated CD8 T lymphocytes, most of which are responding to EBV-infected cells.

Klebsiella pneumoniae is among the most common Gram-negative bacteria encountered by physicians worldwide and accounts for 0.5-5.0% of all cases of pneumonia. This organism can cause extensive pulmonary necrosis and frequent cavitation.It is one of the causes that could be suspected when there is cavitatory pneumonia with or without a bulging fissure sign. Often, there can be extensive lobar opacification with air bronchograms.A helpful feature which may help to distinguish from pneumococcal pneumonia is that Klebsiella pneumoniae develops cavitation in 30-50% of cases (in comparison, cavitation is rare in pneumococcal pneumonia). This occurs early and progresses quickly.

E.Colistrain 0157 causes enterohaemorrhagic diarrhoea and can be followed by haemolytic uraemic syndrome (renal failure, haemolytic anaemia and thrombocytopenia).

The incubation period for Chickenpox is 7-23 days (usually around 2 weeks).Incubation period of botulism is 18-36 hoursIncubation period of Meningococcaemia is 1-7 days.Incubation period of Gonorrhoea is 3-5 days.Incubation period of Hepatitis A is 3-5 weeks.Other infectious with an incubation period of between 1 and 3 weeks are:Whooping cough (7-10 days)Brucellosis (7-21 days)Leptospirosis (7-12 days)Malaria (7-40 days depending on strain)Typhoid (8-21 days)Measles (10-18 days)Mumps (14-18 days)Rubella (14-21 days)

Hepatitis A usually doesn’t pose a special risk to a pregnant woman or her baby. Maternal infection doesn’t result in birth defects, and a mother typically doesn’t transmit the infection to her baby. HAV is almost always transmitted by the faecal-oral route and is usually acquired through close personal contact or via contaminated food.When a woman has chickenpox in the first 20 weeks of pregnancy, there is a 1 in 50 chance for the baby to develop a set of birth defects. This is called the congenital varicella syndrome. It includes scars, defects of muscle and bone, malformed and paralyzed limbs, small head size, blindness, seizures, and intellectual disability.TORCH Syndrome refers to infection of a developing foetus or newborn by any of a group of infectious agents. “TORCH” is an acronym meaning (T)toxoplasmosis, (O)ther Agents, (R)ubella (also known as German Measles), (C)ytomegalovirus, and (H)erpes Simplex.Infection with any of these agents may cause a constellation of similar symptoms in affected newborns. These may include fever; difficulties feeding; small areas of bleeding under the skin, causing the appearance of small reddish or purplish spots; enlargement of the liver and spleen (hepatosplenomegaly); yellowish discoloration of the skin, whites of the eyes, and mucous membranes (jaundice); hearing impairment; abnormalities of the eyes; and other symptoms and findings.

Cholera has an incubation period of 12 hours to 6 days.Other infectious disease that have an incubation period of less than 1 week include:Staphylococcal enteritis (1-6 hours)Salmonella enteritis (12-24 hours)Botulism (18-36 hours)Gas gangrene (6 hours to 4 days)Scarlet fever (1-4 days)Diphtheria (2-5 days)Gonorrhoea (3-5 days)Yellow fever (3-6 days)Meningococcaemia (1-7 days)Brucellosis has an incubation period of 7-21 days.Measles has an incubation period of 14-18 days.Falciparum malaria usually has an incubation period of 7-14 days. The other forms of malaria have a longer incubation period of 12-40 days.Rubella has an incubation period of 14-21 days.

Klebsiellais a genus of non-motile,Gram-negative, rod-shaped bacteriawith a prominent polysaccharide-based capsule. They are routinely found in the nose, mouth and gastrointestinal tract as normal flora, however, they can also behave as opportunistic pathogens.Infections with Klebsiella spp. areusually nosocomial. They are an important cause of ventilator-associated pneumonia (VAP), urinary tract infection, wound infection and bacteraemia. Outbreaks of infections with Klebsiellaspp. in high-dependency units have been described and are associated with septicaemia and high mortality rates. Length of hospital stay and performance of invasive procedures are risk factors forKlebsiellainfections.Primary pneumonia withKlebsiella pneumoniaeis a rare,severe, community-acquired infection associated with a poor outcome.Klebsiella rhinoscleromatis causes a progressive granulomatous infection of the nasal passages and surrounding mucous membranes. This infection is mainly seen in the tropics.Klebsiella ozanae is a recognised cause of chronic bronchiectasis.Klebsiella organisms are resistant to multiple antibiotics including penicillins. This is thought to be a plasmid-mediated property. Agents with high intrinsic activity againstKlebsiellapneumoniaeshould be selected for severely ill patients. Examples of such agents include third-generation cephalosporins (e.g cefotaxime), carbapenems (e.g. imipenem), aminoglycosides (e.g. gentamicin), and quinolones (e.g. ciprofloxacin). These agents may be used as monotherapy or combination therapy. Aztreonam may be used in patients who are allergic to beta-lactam antibiotics.Species with ESBLs (Extended spectrum beta-lactamase) are resistant to penicillins and also cephalosporins such as cefotaxime and ceftriaxone.

Infectious mononucleosis can be diagnosed using specific EBV antibodies and a variety if unrelated non-EBV heterophile antibodies. These antibodies can be detected by two main screening tests:The monospot test uses horse red blood cells. It agglutinates in the presence of heterophile antibodies.Sheep red blood cells is used in Paul-Bunnell test. The blood agglutinates in the presence of heterophile antibodies.

If a patient presents with one of the following types of wounds, they are at risk of contracting tetanus and should be vaccinated immediately:1) Contaminated puncture-type wounds from gardening and farming (as they may contain tetanus spores)2) Wounds containing foreign bodies3) Open (compound) fractures4) Wounds or burns with sepsis5) Animal bites and scratches (animal saliva does not contain tetanus spores unless the animal was routing in soil or lives in an agriculture setting)Extremely high-risk tetanus-prone wounds are any of the above wounds with one of the following:1) Any wound contaminated by materials containing tetanus spores, e.g., soil, manure2) Burns or wounds with extensive devitalised tissue3) Wounds or burns with surgical intervention delayed for more than six hours even if the initial injury was not heavily contaminatedThe CDC recommends that adults who have never been vaccinated for tetanus receive a quick shot of the tetanus vaccine along with a booster dose ten years later. A tetanus-prone wound in an unvaccinated individual should also receive a high dose of tetanus immunoglobulin. The injected antibodies will prevent tetanus infection as the patient does not have any pre-existing antibodies against the disease.In this case, the patient has a high risk, contaminated wound. He should receive a high dose of tetanus immunoglobulin along with the tetanus vaccine. (The preventative dose of tetanus immunoglobulin is 250 IU in most cases unless over 24 hours have passed since the injury or the wound is heavily contaminated, then 500 IU should be given.) His physician also needs to be contacted to arrange the remainder of the course as indicated in this case.

A normal CD4 count ranges from 500-1000 cells/mm3.At CD4 count of less than 350 cells/mm3 treatment with anti-retroviral therapy should be considered.At a CD4 count of >200 cells/mm3 AIDS is diagnosed.

Chickenpox (varicella zoster) is a highly contagious airborne disease and has an incubation period of between 7-21 days. It often has a prodromal phase when there is a fever, aches and headaches, dry cough, and sore throat before onset of rash.Some recognized complications of chickenpox are:OrchitisHepatitisPneumoniaEncephalitisInfected spotsOtitis mediaMyocarditisGlomerulonephritisAppendicitisPancreatitisTreatment is symptomatic and includes using paracetamol to manage fever. There is a link between use of ibuprofen in patients with chicken-pox and necrotizing fasciitis so Ibuprofen should NOT be used. An emollient and antihistamine can be used to ease the itchy rash and oral hydration is encouraged.

The following are the NICE guidelines on the management of bacterial conjunctivitis:- Infective conjunctivitis is a self-limiting illness that usually settles without treatment within 1-2 weeks. If symptoms persist for longer than two weeks they should return for review.- Seek medical attention urgently if marked eye pain or photophobia, loss of visual acuity, or marked redness of the eye develop.- Remove contact lenses, if worn, until all symptoms and signs of infection have completely resolved and any treatment has been completed for 24 hours.- Lubricant eye drops may reduce eye discomfort; these are available over the counter, as well as on prescription.- Clean away infected secretions from eyelids and lashes with cotton wool soaked in water.- Wash hands regularly, particularly after touching the eyes.- Avoid sharing pillows and towels.- It is not necessary to exclude a child from school or childcare if they have infective conjunctivitis, as mild infectious illnesses should not interrupt school attendance. An exception would be if there is an outbreak of infective conjunctivitis, when advice should be sought from the Health Protection Agency by the school. – Adults who work in close contact with others, or with vulnerable patients, should avoid such contact until the discharge has settled.

Hepatitis B surface antigen (HBsAg) is a protein on the surface of the hepatitis B virus, that is the first serologic marker to appear in a new acute infection.It can be detected as early as 1 week and as late as 9 weeks. It can be detected in high levels in serum during acute or chronic hepatitis B virus infection. The presence of HBsAg indicates that the person is infectious. The body normally produces antibodies to HBsAg as part of the normal immune response to infection. HBsAg is the antigen used to make hepatitis B vaccine.Hepatitis B surface antibody (anti-HBs) indicates recovery and immunity from the hepatitis B virus infection. Anti-HBs also develops in a person who has been successfully vaccinated against hepatitis B.Total hepatitis B core antibody (anti-HBc): Appears at the onset of symptoms in acute hepatitis B and persists for life. The presence of anti-HBc indicates previous or ongoing infection with hepatitis B virus in an undefined time frame. It is not present following hepatitis B vaccination.IgM antibody to hepatitis B core antigen (IgM anti-HBc) indicates recent infection with hepatitis B virus (<6 months). Its presence indicates acute infection.The following table summarises the presence of hepatitis B markers according to each situation:Susceptible to infection:HBsAg = NegativeAnti-HBc = NegativeAnti-HBs = NegativeImmune due to natural infection:HBsAg = NegativeAnti-HBc = PositiveAnti-HBs = PositiveImmune due to vaccination:HBsAg = NegativeAnti-HBc = NegativeAnti-HBs = PositiveAcute infection:HBsAg = PositiveAnti-HBc = PositiveAnti-HBs = NegativeIgM anti-HBc = PositiveChronic infection:HBsAg = PositiveAnti-HBc = PositiveAnti-HBs = NegativeIgM anti-HBc = Negative

Legionella pneumophilais a Gram negative bacterium that is found in natural water supplies and in the soil, transmitted predominantly via inhalation of aerosols generated from contaminated water (direct person-to-person spread of infected patients does not occur). It is the cause of Legionnaires’ disease. Outbreaks of Legionnaires’ disease have been linked to poorly maintained air conditioning systems, whirlpool spas and hot tubs.The clinical features of the pneumonic form of Legionnaires’ disease include:Mild flu-like prodrome for 1-3 daysCough (usually non-productive and occurs in approximately 90%)Pleuritic chest painHaemoptysisHeadacheNausea, vomiting and diarrhoeaAnorexiaLegionella pneumophilainfections can be successfully treated with macrolide antibiotics, such as erythromycin, or quinolones, such as ciprofloxacin. Tetracyclines, such as doxycycline, can also be used.The syndrome of inappropriate antidiuretic hormone secretion (SIADH) can occur with Legionnaires’ disease and will result in hyponatraemia as is seen in this case.Legionella pneumophilainfections are resistant to amoxicillin but can be successfully treated with macrolide antibiotics, such as erythromycin, or quinolones, such as ciprofloxacin. Tetracyclines, such as doxycycline, can also be used. The majority of cases of Legionnaires’ disease are caused by Legionella pneumophila, however many other species of Legionella have been identified.Legionella longbeachae is another less commonly encountered species that has also been implicated in outbreaks. It is predominantly found in soil and potting compost, and has caused outbreaks of Pontiac fever, the non-respiratory and less severe variant of Legionnaires’ disease.

Urgent referral to ophthalmology is indicated if the patient with conjunctivitis has any of the following:Suspected gonococcal or chlamydial conjunctivitisCorneal involvement associated with soft contact lens useSevere disease indicated by presence of a pseudomembraneConjunctivitis associated with rheumatoid arthritis or in immunocompromised patient. Ophthalmia neonatorum.Possible herpes infection.Had recent intraocular surgery. A red flag indicating a serious cause of red eye.Suspected periorbital or orbital cellulitis.Bilateral conjunctivitis is not an indication for urgent referral to ophthalmology.

The measles virus is an enveloped virus classified in the genusMorbillivirus.Measles is highly contagious and spreads by aerosol. Initial replication takes place in the mucosal cells of the respiratory tract; measles virus then replicates in the local lymph nodes and spreads systemically. The virus circulates in the T and B cells and monocytes, until eventually the lungs, gut, bile duct, bladder, skin, and lymphatic organs are involved. After an incubation period of 7 to 10 days, there is an abrupt onset, with symptoms of sneezing, runny nose and cough, red eyes, and rapidly rising fever. About 2 to 3 days later, a maculopapular rash appears on the head and trunk. Koplik spots, lesions on the oral mucosa consisting of irregular red spots, with a bluish white speck in the centre, generally appear 2 to 3 days before the rash and are diagnostic.Measles is easily diagnosed clinically, so few requests for laboratory identification are made. The virus is fragile and must be handled carefully. The specimens of choice are from the nasopharynx and urine, but the virus can only be recovered from these sources in the early stages of infection. The virus grows on PMK cells, causing the formation of distinctive spindle-shaped or multinucleated cells.

Helicobacter pylori is a curved, non-spore forming, Gram-negative bacteria that is primarily linked to gastric infections. Once acquired, it colonizes the stomach for a long time and can cause a low-grade inflammatory process, producing a chronic superficial gastritis.H. pylori can be recovered from gastric biopsy materials. Samples must be transported quickly to the laboratory.Helicobacter infections usually are identified by nonculture methods. H. pylori can be presumptively identified in a gastric biopsy specimen by testing for the presence of a rapid urease reaction.Serologic testing is an important screening method for the diagnosis of H. pylori infection. It can also be diagnosed by faecal antigen detection, microscopic examination of stained gastric tissue, and DNA amplification tests.

Endocarditis is infective or non infective inflammation (marantic endocarditis) of the inner layer of the heart and it often involves the heart valves.Risk factors include:Prosthetic heart valvesCongenital heart defectsPrior history of endocarditisRheumatic feverIllicit intravenous drug useIn the presentation of endocarditis, the following triad is often quoted:Persistent feverEmbolic phenomenaNew or changing murmurA combination of vancomycin, rifampicin and gentamicin is advised if the patient has a cardiac prostheses, is penicillin allergic, or if methicillin-resistant Staphylococcus aureus (MRSA) is suspected. In this case the patient has a prosthetic valve making this the most appropriate initial treatment regimen.Flucloxacillin and gentamicin are current recommended by NICE and the BNF for the initial ‘blind’ therapy in endocarditis. This patient has prostheses and this is not the most appropriate initial treatment regimen.Other features that may be present include heart failure, splenomegaly, finger clubbing, renal features (haematuria, proteinuria, nephritis), and vasculitic features (splinter haemorrhages, Osler’s nodes, Janeway lesions, Roth’s spots).

Hyperacute bacterial conjunctivitis is a severe, sight-threatening ocular infection that warrants immediate ophthalmic work-up and management. The infection has an abrupt onset and is characterized by a copious yellow-green purulent discharge that reaccumulates after being wiped away. Typically caused by infection with Neisseria gonorrhoeae.

According to the CDC definition, a patient co-infected with HIV can be diagnosed with AIDS if he or she has:A CD4 T-cell count of less than 200 cells/mm3 or;A CD4 T-cell percentage of total lymphocytes of less than 15% or;An AIDS defining infectionA Streptococcal throat infection is not an AIDS defining infection.A normal CD4 count ranges from 500-1000 cells/mm3. A CD4 (not CD8) count of less than 200 cells/mm3 is AIDS defining.The CD4 count can vary from day to day and depending upon the time that the blood test is taken. It can also be affected by the presence of other infections or illnesses. Treatment with anti-retroviral therapy should be considered at CD4 count of less than 350 cells/mm3.Serum concentrations of the p24 antigen (the viral protein that makes up most of the core of the HIV) are usually high in the first few weeks after human immunodeficiency virus (HIV) infection and testing for p24 antigen is therefore a useful way of diagnosing very early infection.

Acute mastoiditis is a complication (rare) of acute otitis media (AOM) and the commonest causative organism is Streptococcus pneumoniae.Generally, acute mastoiditis presents with:PyrexiaRecent history of AOMMastoid swelling and erythemaOtalgiaOtorrhoea and perforation of tympanic membranePost-auricular painProtrusion of the ears

Treatment should be commenced with antibiotics immediately before laboratory confirmation due to the potentially life-threatening nature of the disease.In a hospital setting, 2g of IV ceftriaxone (80 mg/kg for a child) or IV cefotaxime (2 g adult; 80 mg/kg child) are the drugs of choice. In the prehospital setting, IM benzylpenicillin can be given as an alternative.

Conjunctivitis is the most common neonatal manifestation of Chlamydia trachomatis infection. The second commonest neonatal manifestation is pneumoniaOphthalmia neonatorum refers to any conjunctivitis in the newborn period, irrespective of causative organism. Presently, chlamydia is the single most common cause, accounting for up to 40% of cases. Ophthalmia neonatorum caused by chlamydia typically presents 5 to 14 days after birth with unilateral or bilateral watery discharge that progressively becomes more copious and purulent. There is no associated risk of ulceration and perforation, and the eyes are less inflamed.

The following are organisms that are capable of producing acute, bloody diarrhoea:- Campylobacter jejuni- Escherichia coli O157:H7- Salmonella species- Shigella species- Yersinia species- Entamoeba histolyticaOther E. coli strains, Giardia, Vibrio, and other parasites are associated with watery, but not bloody, diarrhoea.

The most frequent cause of red eye is conjunctivitis. It is caused by inflammation of the conjunctiva which can be infective or allergic and accounts for about 35% of all eye problems presenting to general practice.Viral conjunctivitis is commonly caused by adenoviruses and it is the most common infectious conjunctivitis.The common bacterial causes of conjunctivitis are Haemophilus influenzae, Streptococcus pneumoniae, and Staphylococcus aureus.The clinical features of infective conjunctivitis include:Acute onset of conjunctival erythemaFeeling ‘grittiness’, ‘foreign body’ or ‘burning’ sensation in the eye.Watering and discharge which may cause transient blurring of visionThe discharge for viral conjunctivitis is less than that of bacterial conjunctivitis and usually watery.

Escherichia coli is a Gram-negative, non-spore forming, facultative anaerobic, rod-shaped bacterium. Although some can cause serious food poisoning, most serotypes are harmless.Escherichia coli is transmitted via the faeco-oral route.

Helicobacter pylori is a curved or helix-shaped, non-spore forming, Gram-negative, microaerophilic bacteria. It is motile, having multiple flagella at one pole. It has a lipopolysaccharide component in its outer membrane.

Clostridium difficile, a Gram-positive, anaerobic, spore forming bacteria is present in the gut of approximately 3% of healthy adults (2012 UK HPA estimates). Following use of broad spectrum antibiotics, which alter normal gut flora, Clostridium difficile associated diarrhoea (CDAD) occurs.About 80% of Clostridium difficile infections are seen in people over the age of 65 and its main clinical features are:Abdominal cramps, severe bloody and/or watery diarrhoea, offensive smelling diarrhoea, and fever.

Escherichia coli O157 is a serotype of Escherichia coli.The Escherichia coliO157 strain is ‘enterohaemorrhagic’ and causes severe forms of acute haemorrhagic diarrhoea. It can also cause non-haemorrhagic diarrhoea. Incubation period of Escherichia coli O157 is usually 3-4 days and bloody diarrhoea usually begins on the 3rd or 4th day of the infection.Infections with Escherichia coliO157 are more common during the warmer months than in winter.Haemolytic uraemic syndrome develops in approximately 6% of patients. It is commonly seen in children and in the elderly. Escherichia coli O157 can also cause:Haemorrhagic colitisHaemolytic uraemic syndromeThrombotic thrombocytopenic purpura but not immune thrombocytopenic purpura.