The current incidence in the United States is somewhere around 0.5% per year; overall, the incidence rate for developed world falls between 0.2–0.7%. In developing countries, the incidence of omphalitis varies from 2 to 7 for 100 live births. There does not appear to be any racial or ethnic predilection.

Like many bacterial infections, omphalitis is more common in those patients who have a weakened or deficient immune system or who are hospitalized and subject to invasive procedures. Therefore, infants who are premature, sick with other infections such as blood infection (sepsis) or pneumonia, or who have immune deficiencies are at greater risk. Infants with normal immune systems are at risk if they have had a prolonged birth, birth complicated by infection of the placenta (chorioamnionitis), or have had umbilical catheters.

Gram negative bacterial species are responsible for approximately 24% of all cases of healthcare-associated bacteremia and 45% of all cases of community-acquired bacteremia. In general, gram negative bacteria enter the bloodstream from infections in the respiratory tract, genitourinary tract, gastrointestinal tract, or hepatobiliary system. Gram-negative bacteremia occurs more frequently in elderly populations (65 years or older) and is associated with higher morbidity and mortality in this population.

"E.coli" is the most common cause of community-acquired bacteremia accounting for approximately 75% of cases. E.coli bacteremia is usually the result of a urinary tract infection. Other organisms that can cause community-acquired bacteremia include "pseudomonas aeruginosa", "klebsiella pneumoniae", and "proteus mirabilis". "Salmonella" infection, despite mainly only resulting in gastroenteritis in the developed world, is a common cause of bacteremia in Africa. It principally affects children who lack antibodies to Salmonella and HIV+ patients of all ages.

Among healthcare-associated cases of bacteremia, gram negative organisms are an important cause of bacteremia in the ICU. Catheters in the veins, arteries, or urinary tract can all create a way for gram negative bacteria to enter the bloodstream. Surgical procedures of the genitourinary tract, intestinal tract, or hepatobiliary tract can also lead to gram negative bacteremia. "Pseudomonas" and "enterobacter" species are the most important causes of gram negative bacteremia in the ICU.

There are several risk factors that increase the likelihood of developing bacteremia from any type of bacteria. These include:

- HIV infection

- Diabetes Mellitus

- Chronic hemodialysis

- Solid organ transplant

- Stem cell transplant

- Treatment with glucocorticoids

- Liver failure

Acute infectious thyroiditis is very rare, with it only accounting for about 0.1–0.7% of all thyroiditis. Large hospitals tend to only see two cases of AIT annually. For the few cases of AIT that are seen the statistics seem to show a pattern. AIT is found in children and young adults between the ages of 20 and 40. The occurrence of the disease in people between 20 and 40 is only about 8% with the other 92% being in children. Men and women are each just as likely to get the disease. If left untreated, there is a 12% mortality rate.

People with recurrent boils are as well more likely to have a positive family history, take antibiotics, and to have been hospitalised, anemic, or diabetic; they are also more likely to have associated skin diseases and multiple lesions.

Other causes include poor immune system function such as from HIV/AIDS, diabetes, malnutrition, or alcoholism. Poor hygiene and obesity have also been linked. It may occur following antibiotic use due to the development of resistance to the antibiotics used. An associated skin disease favors recurrence. This may be attributed to the persistent colonization of abnormal skin with "S. aureus" strains, such as is the case in persons with atopic dermatitis.

Boils which recur under the arm, breast or in the groin area may be associated with hidradenitis suppurativa (HS).

Despite the thyroid gland being extremely resistant to infection, it is still susceptible to infection by various bacteria. The cause can be almost any bacterium. "Staphylococcus aureus", "Streptococcus pyogenes", "Staphylococcus epidermidis", and "Streptococcus pneumoniae" in descending order are the organisms most commonly isolated from acute thyroiditis cases in children. Other aerobic organisms are "Klebsiella sp", "Haemophilus influenza", "Streptococcus viridans", "Eikenella corrodens", "Enterobacteriaceae", and "salmonella sp".

Occurrences of AIT are most common in patients with prior thyroid disease such as Hashimoto's thyroiditis or thyroid cancer. The most common cause of infection in children is a congenital abnormality such as pyriform sinus fistula. In most cases, the infection originates in the piriform sinus and spreads to the thyroid via the fistula. In many reported cases of AIT the infection occurs following an upper respiratory tract infection. One study found that of the reported cases of AIT, 66% occurred after an acute illness involving the upper respiratory tract. Although the rates of infection are still very low, cases of AIT have been on the rise in recent years due to the higher occurrence of immune-compromised patients.

Other causes of AIT are commonly due to contamination from an outside source and are included below.

- Repeated fine needle aspirates

- Perforation of esophagus

- Regional infection

"Other infections include:"

- "Closed-space infections of the fingertips, known as paronychia."

The main coagulase-positive staphylococcus is Staphylococcus aureus, although not all strains of Staphylococcus aureus are coagulase positive. These bacteria can survive on dry surfaces, increasing the chance of transmission. S. aureus is also implicated in toxic shock syndrome; during the 1980s some tampons allowed the rapid growth of S. aureus, which released toxins that were absorbed into the bloodstream. Any S. aureus infection can cause the staphylococcal scalded skin syndrome, a cutaneous reaction to exotoxin absorbed into the bloodstream. It can also cause a type of septicaemia called pyaemia. The infection can be life-threatening. Problematically, Methicillin-resistant Staphylococcus aureus (MRSA) has become a major cause of hospital-acquired infections, and is being, MRSA has also been recognized with increasing frequency in community-acquired infections. The symptoms of a Staph Infection include a collection of pus, such as a boil or furuncle, or abscess. The area is typically tender or painful and may be reddened or swollen.

During the 1950s there were outbreaks of omphalitis that then led to anti-bacterial treatment of the umbilical cord stump as the new standard of care. It was later determined that in developed countries keeping the cord dry is sufficient, (known as "dry cord care") as recommended by the American Academy of Pediatrics. The umbilical cord dries more quickly and separates more readily when exposed to air However, each hospital/birthing center has its own recommendations for care of the umbilical cord after delivery. Some recommend not using any medicinal washes on the cord. Other popular recommendations include triple dye, betadine, bacitracin, or silver sulfadiazine. With regards to the medicinal treatments, there is little data to support any one treatment (or lack thereof) over another. However one recent review of many studies supported the use of chlorhexidine treatment as a way to reduce risk of death by 23% and risk of omphalitis by anywhere between 27-56% in community settings in underdeveloped countries. This study also found that this treatment increased the time that it would take for the umbilical stump to separate or fall off by 1.7 days. Lastly this large review also supported the notion that in hospital settings no medicinal type of cord care treatment was better at reducing infections compared to dry cord care.

Bacterial infections of the orbit have long been associated with a risk of catastrophic local

sequelae and intracranial spread.

The natural course of the disease, as documented by Gamble (1933), in the pre-antibiotic era,

resulted in death in 17% of patients and permanent blindness in 20%.

Since opportunistic infections can cause severe disease, much emphasis is placed on measures to prevent infection. Such a strategy usually includes restoration of the immune system as soon as possible, avoiding exposures to infectious agents, and using antimicrobial medications ("prophylactic medications") directed against specific infections.

Individuals at higher risk are often prescribed prophylactic medication to prevent an infection from occurring. A patient's risk level for developing an opportunistic infection is approximated using the patient's CD4 T-cell count and sometimes other markers of susceptibility. Common prophylaxis treatments include the following:

Viruses that may cause adenoiditis include adenovirus, rhinovirus and paramyxovirus. Bacterial causes include Streptococcus pyogenes, Streptococcus pneumoniae, Moraxella catarrhalis and various species of Staphylococcus including Staphylococcus aureus.

Common organisms include Group A "Streptococcus" (group A strep), "Klebsiella", "Clostridium", "Escherichia coli", "Staphylococcus aureus," and "Aeromonas hydrophila", and others. Group A strep is considered the most common cause of necrotizing fasciitis.

The majority of infections are caused by organisms that normally reside on the individual's skin. These skin flora exist as commensals and infections reflect their anatomical distribution (e.g. perineal infections being caused by anaerobes).

Sources of MRSA may include working at municipal waste water treatment plants, exposure to secondary waste water spray irrigation, exposure to run off from farm fields fertilized by human sewage sludge or septage, hospital settings, or sharing/using dirty needles. The risk of infection during regional anesthesia is considered to be very low, though reported.

Vibrio vulnificus, a bacterium found in saltwater, is a rare cause.

Orbital cellulitis occurs commonly from bacterial infection spread via the paranasal sinuses. Other ways in which orbital cellulitis may occur is from infection in the blood stream or from an eyelid skin infection. Upper respiratory infection, sinusitis, trauma to the eye, ocular or periocular infection and systemic infection all increase one's risk of orbital cellulitis.

"Staphylococcus aureus", "Streptococcus pneumoniae" and beta-hemolytic streptococci are three bacteria that can be responsible for orbital cellulitis.

- "Staphylococcus aureus" is a gram-positive bacterium which is the most common cause of staphylococcal infections. "Staphylococcus aureus" infection can spread to the orbit from the skin. These organisms are able to produce toxins which promote their virulence which leads to the inflammatory response seen in orbital cellulitis. "Staphylococcus" infections are identified by a cluster arrangement on gram stain. "Staphylococcus aureus" forms large yellow colonies (which is distinct from other Staph infections such as "Staphylococcus epidermidis" which forms white colonies).

- "Streptococcus pneumoniae" is also a gram-positive bacterium responsible for orbital cellulitis due to its ability to infect the sinuses (sinusitis). Streptococcal bacteria are able to determine their own virulence and can invade surrounding tissues causing an inflammatory response seen in orbital cellulitis (similar to "Staphyloccoccus aureus"). Streptococcal infections are identified on culture by their formation of pairs or chains. "Streptococcus pneumoniae" produce green (alpha) hemolysis, or partial reduction of red blood cell hemoglobin.

It is currently believed that bacterial biofilms play an integral role in the harboring of chronic infection by tonsil and adenoid tissue so contributing to recurrent sinusitis and recurrent or persistent ear disease. Also, enlarged adenoids and tonsils may lead to the obstruction of the breathing patterns in children, causing apnea during sleep.

The most common bacteria isolated are Haemophilus influenzae, group A beta-hemolytic Streptococcus, Staphylococcus aureus, Moraxella catarrhalis, and Streptococcus pneumoniea. Heamophilus influenza, Moraxella catarrhalis and Streptococcus pneumonia are the three most resistant pathogens of otitis and rhinosinisitis in children suffering from these diseases.

A skin and skin structure infection (SSSI), also referred to as skin and soft tissue infection (SSTI) or acute bacterial skin and skin structure infection (ABSSSI), is an infection of skin and associated soft tissues (such as loose connective tissue and mucous membranes). The pathogen involved is usually a bacterial species. Such infections often requires treatment by antibiotics.

Until 2008, two types were recognized, complicated skin and skin structure infection (cSSSI) and uncomplicated skin and skin structure infection (uSSSI). "Uncomplicated" SSSIs included simple abscesses, impetiginous lesions, furuncles, and cellulitis. "Complicated" SSSIs included infections either involving deeper soft tissue or requiring significant surgical intervention, such as infected ulcers, burns, and major abscesses or a significant underlying disease state that complicates the response to treatment. Superficial infections or abscesses in an anatomical site, such as the rectal area, where the risk of anaerobic or gram-negative pathogen involvement is higher, should be considered complicated infections. The two categories had different regulatory approval requirements. The uncomplicated category (uSSSI) is normally only caused by "Staphylococcus aureus" and "Streptococcus pyogenes", whereas the complicated category (cSSSI) might also be caused by a number of other pathogens. In cSSSI, the pathogen is known in only about 40% of cases.

Because cSSSIs are usually serious infections, physicians do not have the time for a culture to identify the pathogen, so most cases are treated empirically, by choosing an antibiotic agent based on symptoms and seeing if it works. For less severe infections, microbiologic evaluation via tissue culture has been demonstrated to have high utility in guiding management decisions. To achieve efficacy, physicians use broad-spectrum antibiotics. This practice contributes in part to the growing incidence of antibiotic resistance, a trend exacerbated by the widespread use of antibiotics in medicine in general. The increased prevalence of antibiotic resistance is most evident in methicillin-resistant "Staphylococcus aureus" (MRSA). This species is commonly involved in cSSSIs, worsening their prognosis, and limiting the treatments available to physicians. Drug development in infectious disease seeks to produce new agents that can treat MRSA.

Since 2008, the U.S. Food and Drug Administration has changed the terminology to "acute bacterial skin and skin structure infections" (ABSSSI). The Infectious Diseases Society of America (IDSA) has retained the term "skin and soft tissue infection".

The initial cause of a carbuncle can often not be determined. Triggers that make carbuncle infections more likely include recent incidence of folliculitis; friction from clothing or shaving; having hair pulled out, such as sites where clothing or furniture grab at hairs; generally poor hygiene; poor nutrition; or weakened immunity. Poor health may be a predisposing factor – for example, persons with diabetes and immune system diseases are more likely to develop infections (especially bacterial infections of the leg or foot).

Skin abscesses are common and have become more common in recent years. Risk factors include intravenous drug use with rates reported as high as 65% in this population. In 2005 in the United States 3.2 million people went to the emergency department for an abscess. In Australia around 13,000 people were hospitalized in 2008 for the disease.

Even without treatment they rarely result in death as they will naturally break through the skin.

The bacteria most associated with salpingitis are:

- N. gonorrhoeae

- Chlamydia trachomatis

- Mycoplasma

- Staphylococcus

- Streptococcus

However, salpingitis is usually polymicrobial, involving many kinds of organisms. Other examples of organisms involved are:

- Ureaplasma urealyticum

- Anaerobic and aerobic bacteria

More than 70% of cases are recorded in people with at least one of the following clinical situations: immunosuppression, diabetes, alcoholism/drug abuse/smoking, malignancies, and chronic systemic diseases. For reasons that are unclear, it occasionally occurs in people with an apparently normal general condition.

The infection begins locally at a site of trauma, which may be severe (such as the result of surgery), minor, or even non-apparent.

It is a commonly encountered otorhinolaryngological (ENT) emergency.

The number of new cases per year of peritonsillar abscess in the United States has been estimated approximately at 30 cases per 100,000 people. In a study in Northern Ireland, the number of new cases was 10 cases per 100,000 people per year.

In Denmark, the new number of new cases is higher and reaches 41 cases per 100,000 people per year. Younger children who develop a peritonsillar abscess are often immunocompromised and in them, the infection can cause airway obstruction.

Over one million cases of acute salpingitis are reported every year in the US, but the number of incidents is probably larger, due to incomplete and untimely reporting methods and that many cases are reported first when the illness has gone so far that it has developed chronic complications. For women age 16–25, salpingitis is the most common serious infection. It affects approximately 11% of females of reproductive age.

Salpingitis has a higher incidence among members of lower socioeconomic classes. However, this is thought of being an effect of earlier sex debut, multiple partners, and decreased ability to receive proper health care rather than any independent risk factor for salpingitis.

As an effect of an increased risk due to multiple partners, the prevalence of salpingitis is highest for people age 15–24 years. Decreased awareness of symptoms and less will to use contraceptives are also common in this group, raising the occurrence of salpingitis.