Streptococci may be divided into alpha and beta haemolytic types

Alpha haemolytic streptococci

The most important alpha haemolytic streptococcus is Streptococcus pneumoniae (pneumococcus). Pneumococcus is a common cause of pneumonia, meningitis and otitis media. Another clinical example is Streptococcus viridans

Beta haemolytic streptococci

These can be subdivided into group A and B

Group A

most important organism is Streptococcus pyogenes
responsible for erysipelas, impetigo, cellulitis, type 2 necrotizing fasciitis and pharyngitis/tonsillitis
immunological reactions can cause rheumatic fever or post-streptococcal glomerulonephritis
erythrogenic toxins cause scarlet fever

Group B

Streptococcus agalactiae may lead to neonatal meningitis and septicaemia

Based on the history and findings, the most likely causative organism is cryptosporidium. It can cause severe, chronic, and possibly fatal diarrhoea in immunocompromised patients.

In patients with HIV/AIDS, clinical manifestations of cryptosporidiosis vary with the degree of immune compromise. Those with CD4 cell counts above 180–200/μL may be asymptomatic or develop self-limiting diarrhoeal illness. However, patients with advanced AIDS (CD4 cell counts <50/μL) can have severe diarrhoea that can persist for several months, resulting in severe dehydration, weight loss and malnutrition, extended hospitalizations, and mortality. In addition, patients with advanced AIDS are at greater risk of developing extraintestinal infection, particularly of the biliary, pancreatic, and respiratory tracts.

Hepatitis A is a viral liver disease that can cause mild to severe illness. The hepatitis A virus (HAV) is transmitted through ingestion of contaminated food and water or through direct contact with an infectious person.
The risk of hepatitis A infection is associated with a lack of safe water, and poor sanitation and hygiene (such as dirty hands). Unlike hepatitis B and C, hepatitis A does not cause chronic liver disease and is rarely fatal, but it can cause debilitating symptoms and fulminant hepatitis (acute liver failure), which is often fatal.
Prodrome
In the prodrome, patients may have mild flulike symptoms of anorexia, nausea and vomiting, fatigue, malaise, low-grade fever (usually < 39.5°C), myalgia, and mild headache. Smokers often lose their taste for tobacco, like persons presenting with appendicitis. Icteric phase
In the icteric phase, dark urine appears first (bilirubinuria). Pale stool soon follows, although this is not universal. Jaundice occurs in most (70%-85%) adults with acute HAV infection; it is less likely in children and is uncommon in infants. The degree of icterus also increases with age. Abdominal pain occurs in approximately 40% of patients. Itching (pruritus), although less common than jaundice, is generally accompanied by jaundice.

Arthralgias and skin rash, although also associated with acute HAV infection, are less frequent than the above symptoms. Rash more often occurs on the lower limbs and may have a vasculitic appearance.

Relapsing hepatitis A
Relapsing hepatitis A is an uncommon sequela of acute infection, is more common in elderly persons, and is characterized by a protracted course of symptoms of the disease and a relapse of symptoms and signs following apparent resolution.

Clostridium difficile is an anaerobic, gram-positive, spore-forming bacillus that is responsible for the majority of cases of antibiotic-associated diarrhoea in surgical patients. While the spectrum of disease may range from asymptomatic carrier state to life-threatening toxic megacolon, the typical presentation in surgical patients is diarrhoea developing in the first few days after initiation of antibiotic therapy, including single-dose prophylactic perioperative antibiotics.
In routine cases with bile spillage, surgeons generally do use antibiotic prophylaxis; 80% give one dose only while 88% give one or more prophylactic doses of an antibiotic. Co-amoxiclav is the most commonly used antibiotic in all settings.

Giardia is a microscopic parasite that causes the diarrheal illness known as giardiasis. Giardia (also known as Giardia intestinalis, Giardia lamblia, or Giardia duodenalis) is found on surfaces or in soil, food, or water that has been contaminated with faeces from infected humans or animals.

Giardia is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it tolerant to chlorine disinfection. While the parasite can be spread in different ways, water (drinking water and recreational water) is the most common mode of transmission.

Signs and symptoms may vary and can last for 1 to 2 weeks or longer. In some cases, people infected with Giardia have no symptoms.

Acute symptoms include:

Diarrhoea
Gas
Greasy stools that tend to float
Stomach or abdominal cramps
Upset stomach or nausea/vomiting
Dehydration (loss of fluids)
Other, less common symptoms include itchy skin, hives, and swelling of the eye and joints. Sometimes, the symptoms of giardiasis might seem to resolve, only to come back again after several days or weeks. Giardiasis can cause weight loss and failure to absorb fat, lactose, vitamin A and vitamin B12.

In children, severe giardiasis might delay physical and mental growth, slow development, and cause malnutrition.

Answer: Yersinia enterocolitica

Yersinia enterocolitica (see the image below) is a bacterial species in the family Enterobacteriaceae that most often causes enterocolitis, acute diarrhoea, terminal ileitis, mesenteric lymphadenitis, and pseudo appendicitis but, if it spreads systemically, can also result in fatal sepsis. Symptoms of Y enterocolitica infection typically include the following:

Diarrhoea – The most common clinical manifestation of this infection; diarrhoea may be bloody in severe cases

Low-grade fever

Abdominal pain – May localize to the right lower quadrant

Vomiting – Present in approximately 15-40% of cases

Mesenteric adenitis, mesenteric ileitis, and acute pseudo appendicitis
These manifestations are characterized by the following symptoms (although nausea, vomiting, diarrhoea, and aphthous ulcers of the mouth can also occur):

Fever

Abdominal pain

Tenderness of the right lower quadrant

Leucocytosis

Pseudo appendicitis syndrome is more common in older children and young adults. Patients with Y enterocolitica infection often undergo appendectomy; several Scandinavian studies suggested a prevalence rate of 3.8-5.6% for infection with Y enterocolitica in patients with suspected appendicitis.

Analysis of several common-source outbreaks in the United States found that 10% of 444 patients with symptomatic, undiagnosed Y enterocolitica infection underwent laparotomy for suspected appendicitis.

Human clinical Y enterocolitica infections ensue after ingestion of the microorganisms in contaminated food or water or by direct inoculation through blood transfusion.

Y enterocolitica is potentially transmitted by contaminated unpasteurized milk and milk products, raw pork, tofu, meats, oysters, and fish. Outbreaks have been associated with raw vegetables; the surface of vegetables can become contaminated with pathogenic microorganisms through contact with soil, irrigation water, fertilizers, equipment, humans, and animals.

Pasteurized milk and dairy products can also cause outbreaks because Yersinia can proliferate at refrigerated temperatures.

Animal reservoirs of Y enterocolitica include swine (principle reservoir), dogs, cats, cows, sheep, goats, rodents, foxes, porcupines, and birds.

Reports of person-to-person spread are conflicting and are generally not observed in large outbreaks. Transmission via blood products has occurred, however, and infection can be transmitted from mother to new-born infant. Faecal-oral transmission among humans has not been proven.

Clostridioides difficile (formerly Clostridium difficile) colitis results from a disturbance of the normal bacterial flora of the colon, colonization by C difficile, and the release of toxins that cause mucosal inflammation and damage. Antibiotic therapy is the key factor that alters the colonic flora. C difficile infection (CDI) occurs primarily in hospitalized patients.
The diagnosis of C difficile colitis should be suspected in any patient with diarrhoea who has received antibiotics within the previous 3 months, has been recently hospitalized, and/or has an occurrence of diarrhoea within 48 hours or more after hospitalization. In addition, C difficile can be a cause of diarrhoea in community dwellers without previous hospitalization or antibiotic exposure

The following recommendations on Clostridium difficile infection (CDI) were released on February 2018 by the Infectious Diseases Society of America (ISDA) and Society for Healthcare Epidemiology of America (SHEA).
Diagnosis (adults)
Patients with unexplained and new-onset ≥3 unformed stools in 24 hours are the preferred target population for testing for CDI.
Use a stool toxin test as part of a multistep algorithm (i.e., glutamate dehydrogenase [GDH] plus toxin; GDH plus toxin, arbitrated by nucleic acid amplification test [NAAT]; or NAAT plus toxin) rather than NAAT alone for all specimens when there are no pre-agreed institutional criteria for patient stool submission.
Use NAAT alone or a multistep algorithm for testing (i.e., GDH plus toxin; GDH plus toxin, arbitrated by NAAT; or NAAT plus toxin) rather than a toxin test alone when there are pre-agreed institutional criteria for patient stool submission.
Do not perform repeat testing (within 7 days) during the same episode of diarrhoea and do not test stool from asymptomatic patients, except for epidemiologic studies

Necrosis and ulcers of the colon are a feature of infection with enteroinvasive E. coli (EIEC). It presents with a dysentery-type illness similar to shigellosis.

E. coli have different strains that cause a wide range of conditions. The four main types are:

1. Enteropathogenic E. coli—cause watery diarrhoea, vomiting, and low-grade fever

2. Enteroinvasive E. coli—cause dysentery, large bowel necrosis, and ulcers

3. Enterotoxigenic E. coli—cause traveller’s diarrhoea

4. Enterohaemorrhagic E. coli 0157:H7—cause haemorrhagic colitis, haemolytic uremic syndrome, and thrombotic thrombocytopenic purpura

Answer: Infection with Staphylococcus aureus

Surgical site infections (SSIs) are among the most common healthcare-associated infections, and contribute significantly to patient morbidity and healthcare costs. Staphylococcus aureus is the most common microbial cause. The epidemiology of S. aureus is changing with the dissemination of newer clones and the emergence of mupirocin resistance. Pre-operative screening, using culture- or molecular-based methods, and subsequent decolonization of patients who are positive for methicillin-susceptible S. aureus and methicillin-resistant S. aureus (MRSA) reduces SSIs and hospital stay. This applies especially to major clean surgery, such as cardiothoracic and orthopaedic, involving the insertion of implanted devices. However, it requires a multi-disciplinary approach coupled with patient education. Universal decolonization pre-operatively without screening for S. aureus may compromise the capacity to monitor for the emergence of new clones of S. aureus, contribute to mupirocin resistance, and prevent the adjustment of surgical prophylaxis for MRSA (i.e. replacement of a beta-lactam agent with a glycopeptide or alternative).

A surgical site infection is an infection that occurs after surgery in the part of the body where the surgery took place. Surgical site infections can sometimes be superficial infections involving the skin only. Other surgical site infections are more serious and can involve tissues under the skin, organs, or implanted material.

Symptoms include:
Redness and pain around the area where you had surgery
Drainage of cloudy fluid from your surgical wound
Fever

Answer: Streptococcus pyogenes

Tonsillitis is inflammation of the pharyngeal tonsils. The inflammation usually extends to the adenoid and the lingual tonsils; therefore, the term pharyngitis may also be used. Most cases of bacterial tonsillitis are caused by group A beta-haemolytic Streptococcus pyogenes (GABHS).

Signs and symptoms
Tonsillitis

Individuals with acute tonsillitis present with the following:
Fever
Sore throat
Foul breath
Dysphagia (difficulty swallowing)
Odynophagia (painful swallowing)
Tender cervical lymph nodes

Airway obstruction may manifest as mouth breathing, snoring, sleep-disordered breathing, nocturnal breathing pauses, or sleep apnoea.

Peritonsillar abscess

Individuals with peritonsillar abscess (PTA) present with the following:
Severe throat pain
Fever
Drooling
Foul breath
Trismus (difficulty opening the mouth)
Altered voice quality (the hot-potato voice)

Treatment of acute tonsillitis is largely supportive and focuses on maintaining adequate hydration and caloric intake and controlling pain and fever.

Corticosteroids may shorten the duration of fever and pharyngitis in cases of infectious mononucleosis (MN). In severe cases of MN, corticosteroids or gamma globulin may be helpful. GABHS infection obligates antibiotic coverage.

Pinworm infection is caused by a small, thin, white roundworm called Enterobius vermicularis. Although pinworm infection can affect all people, it most commonly occurs among children, institutionalized persons, and close-contacts. Pruritus is the main symptom, as there is a lack of tissue invasion. It is rare for individuals to have any signs of systemic sepsis. Pinworm infection is treatable with over-the-counter or prescription medication, but reinfection, which occurs easily, should be prevented

Bacteroides species are anaerobic bacteria that are predominant components of the bacterial florae of mucous membranes and are therefore a common cause of endogenous infections. Bacteroides infections can develop in all body sites, including the CNS, the head, the neck, the chest, the abdomen, the pelvis, the skin, and the soft tissues. Inadequate therapy against these anaerobic bacteria may lead to clinical failure.

These bacteria are resistant to penicillins, mostly through the production of beta-lactamase. Anaerobic bacteria can infect deep wounds, deep tissues, and internal organs where there is little oxygen. These infections are characterized by abscess formation, foul-smelling pus, and tissue destruction. Anaerobes outnumber aerobes by 1000:1 in the large intestine; thus, they play an important role in almost all intra-abdominal infections.

Secondary peritonitis and abdominal abscesses generally occur after entry of enteric organisms into the peritoneal cavity through perforation of the intestine or other viscus as a result of obstruction, infarction, or trauma.

Most visceral abscesses (e.g., hepatic), chronic cholecystitis, perforated and gangrenous appendicitis, postoperative wound infections and abscesses, diverticulitis, and any infection associated with faecal contamination of the abdominal cavity involve both aerobes and anaerobes.

Staphylococcus epidermidis tends to colonise plastic devices (such as the breast implant in this scenario) and forms a biofilm which allows colonisation with other bacterial agents. It is extremely difficult to eradicate the infection once established, and the usual treatment is removal of the device.

Staphylococcus epidermidis is a gram-positive facultative anaerobic bacterium. It is part of the normal human flora, typically the skin flora, and less commonly the mucosal flora. It is also one of the most frequently detected pathogens in infections following implant surgery.

Surgical site infection (SSI) by Staphylococcus aureus is the most likely cause in this scenario. In the UK from 2010–2011, 23% of wound infections were due to S. aureus. Infection with the other organisms, including Streptococcus pyogenes, are much rarer.

Surgical site infections (SSI) comprise up to 20% of all healthcare-associated infections and at least 5% of patients undergoing surgery will develop an SSI as a result. SSIs may occur following a breach in tissue surfaces and allow normal commensals and other pathogens to initiate infection. The organisms are mostly derived from the patient’s own body.

SSIs are a major cause of morbidity and mortality.
Some preoperative measures that may increase the risk of SSI include:
1. Shaving the wound using a razor (disposable clipper preferred)
2. Tissue hypoxia
3. Delayed administration of prophylactic antibiotics in tourniquet surgery

SSIs can be prevented by taking certain precautionary steps pre-, intra-, and postoperatively.

1. Preoperatively:
a. Do not remove body hair routinely
b. If hair needs removal, use electrical clippers (razors increase the risk of infection)
c. Antibiotic prophylaxis if:
– placement of prosthesis or valve
– clean-contaminated surgery
– contaminated surgery

2. Intraoperatively:
a. Prepare the skin with alcoholic chlorhexidine (Lowest incidence of SSI)
b. Cover surgical site with dressing

3. Postoperatively:
a. Prevention of incisional infection by appropriate cleansing, skin care, and moisture management
b.Tissue viability advice for management of surgical wound healing by secondary intention

Clostridioides difficile (C. difficile; formerly known as Clostridium difficile) is a gram-positive rod-shaped bacillus that is commonly involved in antibiotic-associated diarrhoea. As the bacterial spores are difficult to eradicate and easily transmitted (via faecal-oral transmission), the C. difficile infection rate is particularly high among hospitalized patients and residents in long-term care facilities.
Colonization with C. difficile occurs following antibiotic treatment of other diseases, as the bacteria is particularly resistant to antibiotics. The resulting damage to the intestinal flora promotes infection, which may be accompanied by high fever, abdominal pain, and characteristically foul-smelling diarrhoea. The most severe form of C. difficile infection is pseudomembranous colitis, which may lead to ileus, sepsis, and toxic megacolon. In most cases, however, colonization results in asymptomatic carriage rather than symptomatic infection.
Diagnosis is usually made via detection of the C. difficile toxin and/or corresponding genes in stool samples. C. difficile infections are treated with oral vancomycin or oral fidaxomicin. Following diagnosis, strict adherence to hygiene measures and patient isolation is essential, especially in hospitals and other healthcare settings.

Cryptosporidium infection occurs through the faecal-oral route of transmission. It usually lasts for 5–7 days. In immunocompetent patients it is self-limiting (nitazoxanide may be used to shorten the duration). In immunocompromised patients: Antiretroviral therapy to elevate the CD4 cell count/restore the immune system is essential prior to eradication with antiparasitic drugs. Diarrhoea is the main disease. The cysts are typically identified on stool microscopy.

P24 antigen test is used as one of the main investigations in diagnosing HIV seroconversion illness.

Some people experience a short illness soon after they contract HIV. This is known as seroconversion illness, or primary or acute HIV infection. It is the period when someone with HIV is at their most infectious.

HIV seroconversion is symptomatic in 60%–80% of the patients and typically presents as a glandular fever-type illness. Increased symptomatic severity is associated with poorer long-term prognosis. It typically occurs 2–3 weeks after contracting the virus.

Signs and symptoms include:
1. Sore throat
2. Malaise, myalgia, and arthralgia
3. Diarrhoea
4. Maculopapular rash
5. Oral ulcers
6. Lymphadenopathy
7. Meningoencephalitis (rarely)

HIV PCR and p24 antigen test can confirm the diagnosis. The former is the most common and accurate test and consists of both a screening ELISA and a confirmatory western blot assay. P24 antigen test is also used as the mainstay of diagnosis and is usually positive from about 1 week to 3–4 weeks after an infection with HIV.

Streptococcus bovis (S. bovis) bacteria are associated with colorectal cancer and adenoma. S. bovis is currently named S. gallolyticus. 25-80% of patients with S. bovis/gallolyticus bacteraemia have concomitant colorectal tumours. Colonic neoplasia may arise years after the presentation of bacteraemia or infectious endocarditis of S. bovis/gallolyticus. The presence of S. bovis/gallolyticus bacteraemia and/or endocarditis is also related to the presence of villous or tubular-villous adenomas in the large intestine.

Answer: Epstein-Barr virus

The Epstein–Barr virus is one of eight known human herpesvirus types in the herpes family, and is one of the most common viruses in humans. Infection with Epstein-Barr virus (EBV) is common and usually occurs in childhood or early adulthood.
EBV is the cause of infectious mononucleosis, an illness associated with symptoms and signs like:
fever,
fatigue,
swollen tonsils,
headache, and
sweats,
sore throat,
swollen lymph nodes in the neck, and
sometimes an enlarged spleen.

Although EBV can cause mononucleosis, not everyone infected with the virus will get mononucleosis. White blood cells called B cells are the primary targets of EBV infection.
Petechiae on the palate are characteristic of streptococcal pharyngitis but also can be seen in Epstein–Barr virus infection, Arcanobacterium haemolyticum pharyngitis, rubella, roseola, viral haemorrhagic fevers, thrombocytopenia, and palatal trauma.
Despite the fact that infectious mononucleosis is a self-limiting disease, it may cause serious and lethal complications. The mechanism of splenic rupture secondary to infectious mononucleosis has been controversial. It is commonly believed that it is caused by an increase in intra-abdominal pressure or contraction of the diaphragm with vigorous cough, vomiting and defecation, leading to a compression of the spleen. However, Patel et al. argue that it is primarily the result of an expanding subcapsular haematoma which subsequently tears the capsule and leads to hemoperitoneum. Traditionally, rupture of spleen is treated by splenectomy. The rationale is to prevent the chance of sudden death as an early complication of splenic rupture and the risk from blood transfusion.

Answer: Clostridium perfringens

Clostridium perfringens (C. perfringens) is a spore-forming gram-positive bacterium that is found in many environmental sources as well as in the intestines of humans and animals. C. perfringens is commonly found on raw meat and poultry. It prefers to grow in conditions with very little or no oxygen, and under ideal conditions can multiply very rapidly. Some strains of C. perfringens produce a toxin in the intestine that causes illness.
Beef, poultry, gravies, and dried or pre-cooked foods are common sources of C. perfringens infections. C. perfringens infection often occurs when foods are prepared in large quantities and kept warm for a long time before serving. Outbreaks often happen in institutions, such as hospitals, school cafeterias, prisons, and nursing homes, or at events with catered food.
People infected with C. perfringens develop diarrhoea and abdominal cramps within 6 to 24 hours (typically 8 to 12 hours). The illness usually begins suddenly and lasts for less than 24 hours. People infected with C. perfringens usually do not have fever or vomiting. The illness is not passed from one person to another.
Although C. perfringens may live normally in the human intestine, illness is caused by eating food contaminated with large numbers of C. perfringens bacteria that produce enough toxin in the intestines to cause illness.

C. perfringens can survive high temperatures. During cooling and holding of food at temperatures from 54°F–140°F (12°C–60°C), the bacteria grows. It can grow very rapidly between 109°F–117°F (43°C–47°C). If the food is served without reheating to kill the bacteria, live bacteria may be eaten. The bacteria produce a toxin inside the intestine that causes illness.