Individuals with a weak immune system are most at risk. This includes individuals taking immunosuppressive medication, cancer patients, HIV patients, premature babies with very low birth weight, the elderly, etc.

People who are at an increased risk of acquiring particular fungal infections in general may also be at an increased risk of developing fungal meningitis, as the infection may in some cases spread to the CNS. People residing in the Midwestern United States, and Southwestern United States and Mexico are at an increased risk of infection with "Histoplasma" and "Coccidioides", respectively.

Fungal meningitis may be caused by the following (and also other) types of fungi:

- "Candida" - "C. albicans" is the most common "Candida" species causing CNS infection.

- "Coccidioides" - it is endemic to southwestern United States and Mexico. A third of patients presenting with disseminated coccidioidomycosis have developed meningitis.

- "Histoplasma" - occurs in bird and bat droppings and is endemic in parts of the United States, South, and Central America. CNS involvement occurs in 10-20% of disseminated histoplasmosis cases.

- "Blastomyces" - occurs in soil rich in decaying organic matter in the Midwest United States. Meningitis is an unusual manifestation of blastomycosis and can be very difficult to diagnose.

- "Cryptococcus" (Cryptococcal meningitis) - it is thought to be acquired through inhalation of soil contaminated with bird droppings. "C. neoformans" is the most common pathogen to cause fungal meningitis.

- "Aspergillus" - "Aspergillus" infections account for 5% of CNS fungal infections.

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.

There are many different forms on prevention of syphilis and other sexually transmitted diseases in general. Prevention of syphilis includes avoiding contact of bodily fluids with an infected person. This can be particularly difficult because syphilis is usually transmitted by people who are unaware that they have the disease because they do not have any visible sores or rashes that may denote having an infection in general. Being abstinent or having mutually monogamous sex with a person who is uninfected with any type of sexually transmitted disease is the greatest guarantee of not becoming infected with syphilis or any form of a sexually transmitted disease. Using latex condoms can however reduce the risk of obtaining syphilis. In order to prevent further contamination to other individuals, benzathine penicillin is given to any contacts. Washing, douching, or urinating cannot prevent the transmission of a sexually transmitted disease in general.

Individuals obtain syphilis through a variety of circumstances. In general, syphilis can be transmitted from individual to individual through direct contact with sores that are present on the external genitals, vagina, rectum, anus, lips, or mouth. Transmission can occur through any form of sexual contact, including vaginal, anal, and oral sex. In addition, women who are pregnant and infected with syphilis can transmit the disease onto their child as well. If transmission has occurred, it is important to check up immediately with a physician to avoid further damage.

Bats recovering from white-nose syndrome (WNS) may be the first natural occurrence of IRIS, in a report released by the USGS. WNS is typified by a cutaneous infection of the fungus "Pseudogymnoascus destructans" during hibernation, when the immune system is naturally suppressed to conserve energy through the winter. This study suggests that bats undergoing an intense inflammation at the site of infection after a return to euthermia is a form of IRIS.

The prognosis of nocardiosis is highly variable. The state of the host's health, site, duration, and severity of the infection all play parts in determining the prognosis. As of now, skin and soft tissue infections have a 100% cure rate, and pleuropulmonary infections have a 90% cure rate with appropriate therapy. The cure rate falls to 63% with those infected with dissemented nocardiosis, with only half of those surviving infections that cause brain abscess. Additionally, 44% of people who are infected in the spinal cord/brain die, increasing to 85% if that person has an already weakened immune system. Unfortunately, there is not a preventative to nocardiosis. The only recommendation is to protect open wounds to limit access.

Research has shown a link between trichomoniasis and two serious sequelae. Data suggest that:

- Trichomoniasis is associated with increased risk of transmission and infection of HIV.

- Trichomoniasis may cause a woman to deliver a low-birth-weight or premature infant.

- The role of trichomonas infection in causing cervical cancer is unclear, although trichomonas infection may be associated with co-infection with high-risk strains of HPV.

- "T. vaginalis" infection in males has been found to cause asymptomatic urethritis and prostatitis. In the prostate, it may create chronic inflammation that may eventually lead to prostate cancer.

In microbiology, coinfection is the simultaneous infection of a host by multiple pathogen species. In virology, coinfection includes simultaneous infection of a single cell by two or more virus particles. An example is the coinfection of liver cells with Hepatitis B virus and Hepatitis D virus, which can arise incrementally by initial infection followed by superinfection.

Global prevalence or incidence of coinfection among humans is unknown, but it is thought to be commonplace, sometimes more common than single infection. Coinfection with helminths affects around 800 million people worldwide.

Coinfection is of particular human health importance because pathogen species can interact within the host. The net effect of coinfection on human health is thought to be negative. Interactions can have either positive or negative effects on other parasites. Under positive parasite interactions, disease transmission and progression are enhanced and this is also known as syndemism. Negative parasite interactions include microbial interference when one bacterial species suppresses the virulence or colonisation of other bacteria, such as "Pseudomonas aeruginosa" suppressing pathogenic "Staphylococcus aureus" colony formation. The general patterns of ecological interactions between parasite species are unknown, even among common coinfections such as those between sexually transmitted infections. However, network analysis of a food web of coinfection in humans suggests that there is greater potential for interactions via shared food sources than via the immune system.

A globally common coinfection involves tuberculosis and HIV. In some countries, up to 80% of tuberculosis patients are also HIV-positive. The potential for dynamics of these two infectious diseases to be linked has been known for decades. Other common examples of coinfections are AIDS, which involves coinfection of end-stage HIV with opportunistic parasites and polymicrobial infections like Lyme disease with other diseases.

Omphalitis is most commonly caused by bacteria. The culprits usually are "Staphylococcus aureus", "Streptococcus", and "Escherichia coli". The infection is typically caused by a combination of these organisms and is a mixed Gram-positive and Gram-negative infection. Anaerobic bacteria can also be involved.

When properly diagnosed, the mortality of Lemierre's syndrome is about 4.6%. Since this disease is not well known and often remains undiagnosed, mortality might be much higher.

The Jarisch-Herxheimer reaction, which is the response to the body after endotoxins are released by the death of harmful organisms in the human body, starts usually during the first day of antibiotic treatment. The reaction increases the person's body temperature, decreases the overall blood pressure (both systolic and diastolic levels), and results in leukopenia and rigors in the body. This reaction can occur during any treatment of spirochete diseases.

It is important to realize that syphilis can recur. An individual who has had the disease once, even if it has been treated, does not prevent the person from experiencing recurrence of syphilis. Individuals can be re-infected, and because syphilis sores can be hidden, it may not be obvious that the individual is infected with syphilis. In these cases, it is vital to become tested and treated immediately to reduce spread of the infection.

Normally found in soil, these organisms cause occasional sporadic disease in humans and animals throughout the world. Another well publicized find is that of Nocardia as an oral microflora. Nocardia spp. have been reported in the normal gingiva and periodontal pockets along with other species such as "Actinomyces", "Arthromyces" and "Streptomyces" spp.

The usual mode of transmission is inhalation of organisms suspended in dust. Another very common method is that by traumatic introduction, especially in the jaw. This leads to the entrance of Nocardia into the blood stream and the propagation of its pathogenic effects. Transmission by direct inoculation through puncture wounds or abrasions is less common. Generally, nocardial infection requires some degree of immune suppression.

A weakened immune system is a general indicator of someone who is more susceptible to nocardiosis, such as someone who already has a disease that weakens their immune system. Additionally, those with low T-cell counts or other complications involving T-cells can expect to have a higher chance of becoming infected. Besides those with weak immune systems, a local traumatic inoculation can cause nocardiosis, specifically the cutaneous, lymphocutaneous, and subcutaneous forms of the disease.

A study conducted on 452 patients revealed that the genotype responsible for higher IL-10 expression makes HIV infected people more susceptible to tuberculosis infection. Another study on HIV-TB co-infected patients also concluded that higher level of IL-10 and IL-22 makes TB patient more susceptible to Immune reconstitution inflammatory syndrome (IRIS). It is also seen that HIV co-infection with tuberculosis also reduces concentration of immunopathogenic matrix metalloproteinase (MMPs) leading to reduced inflammatory immunopathology.

A minority of cases of infectious mononucleosis is caused by human cytomegalovirus (CMV), another type of herpes virus. This virus is found in body fluids including saliva, urine, blood, and tears. A person becomes infected with this virus by direct contact with infected body fluids. Cytomegalovirus is most commonly transmitted through kissing and sexual intercourse. It can also be transferred from an infected mother to her unborn child. This virus is often "silent" because the signs and symptoms cannot be felt by the person infected. However, it can cause life-threatening illness in infants, HIV patients, transplant recipients, and those with weak immune systems. For those with weak immune systems, cytomegalovirus can cause more serious illnesses such as pneumonia and inflammations of the retina, esophagus, liver, large intestine, and brain. Approximately 90% of the human population has been infected with cytomegalovirus by the time they reach adulthood, but most are unaware of the infection. Once a person becomes infected with cytomegalovirus, the virus stays in his/her body fluids throughout his or her lifetime.

About 90% of cases of infectious mononucleosis are caused by the Epstein–Barr virus, a member of the Herpesviridae family of DNA viruses. It is one of the most commonly found viruses throughout the world. Contrary to common belief, the Epstein–Barr virus is not highly contagious. It can only be contracted through direct contact with an infected person’s saliva, such as through kissing or sharing toothbrushes, cups, etc. About 95% of the population has been exposed to this virus by the age of 40, but only 15–20% of teenagers and about 40% of exposed adults actually become infected.

The suppression of CD4 T cells by HIV (or by immunosuppressive drugs) causes a decrease in the body's normal response to certain infections. Not only does this make it more difficult to fight the infection, it may mean that a level of infection that would normally produce symptoms is instead undetected (subclinical infection). If the CD4 count rapidly increases (due to effective treatment of HIV, or removal of other causes of immunosuppression), a sudden increase in the inflammatory response produces nonspecific symptoms such as fever, and in some cases a worsening of damage to the infected tissue.

There are two common IRIS scenarios. The first is the “unmasking” of an opportunistic infection. The second is the “paradoxical” symptomatic relapse of a prior infection despite microbiologic treatment success. Often in paradoxical IRIS, microbiologic cultures are sterile. In either scenario, there is hypothesized reconstitution of antigen-specific T cell-mediated immunity with activation of the immune system following HIV therapy against persisting antigen, whether present as intact organisms, dead organisms, or debris.

Though these symptoms can be dangerous, they also indicate that the body may now have a better chance to defeat the infection. The best treatment for this condition is unknown. In paradoxical IRIS reactions, the events will usually spontaneously get better with time without any additional therapy. In unmasking IRIS, the most common treatment is to administer antibiotic or antiviral drugs against the infectious organism. In some severe cases, anti-inflammatory medications, such as corticosteroids are needed to suppress inflammation until the infection has been eliminated.

Infections most commonly associated with IRIS include "Mycobacterium tuberculosis" and cryptococcal meningitis. Persons living with AIDS are more at risk for IRIS if they are starting for the first time, or if they have recently been treated for an opportunistic infection (OI). It is generally advised that when patients have low initial CD4 T cell count and opportunistic infection at the time of their HIV diagnosis, they receive treatment to control the opportunistic infections before HAART is initiated approximately two weeks later. This is true for most OIs, except for OIs involving the central nervous system.

Paravaccinia virus originates from livestock infected with bovine papular stomatitis. When a human makes physical contact with the livestock's muzzle, udders, or an infected area, the area of contact will become infected. Livestock may not show symptoms of bovine papular stomatitis and still be infected and contagious. Paravaccinia can enter the body though all pathways including: skin contact by mechanical means, through the respiratory tract, or orally. Oral or respiratory contraction may be more likely to cause systemic symptoms such as lesions across the whole body

A person who has not previously been infected with paravaccinia virus should avoid contact with infected livestock to prevent contraction of disease. There is no commercially available vaccination for cattle or humans against paravaccinia. However, following infection, immunization has been noted in humans, making re-infection difficult. Unlike other pox viruses, there is no record of contracting paravaccinia virus from another human. Further, cattle only show a short immunization after initial infection, providing opportunity to continue to infect more livestock and new human hosts.

There were about 58 million cases of trichomoniasis in 2013. It is more common in women (2.7%) than males (1.4%). It is the most common non-viral STI in the U.S., with an estimated 3.7 million prevalent cases and 1.1 million new cases per year. It is estimated that 3% of the general U.S. population is infected, and 7.5-32% of moderate-to-high risk (including incarcerated) populations.

As is often the case, there are diseases/conditions with signs and symptoms that are similar to actinomycosis. As such, misdiagnoses can occur. Some examples include abscesses caused by grass seeds, woody tongue, bottle jaw, cancerous growths, and irritation caused by lodged objects.

It is unknown what aspects of the natural immune response to HIV may protect someone from superinfection, but it has been shown that cytotoxic lymphocyte responses do not seem to be protective. In addition, it has been demonstrated that superinfection can occur in individuals that demonstrate a robust anti-HIV antibody response. The anti-HIV antibody response broadens and strengthens in individuals post-superinfection.

Taken with the finding that super-infection is common and occurs within and between HIV subtypes it has been suggested that the immune response elicited by primary infection may confer limited protection and raises concerns that HIV-vaccine strategies designed to replicate the natural anti-HIV immune response may have limited effectiveness in preventing new infections. However at the same time, HIV-infected individuals at high risk for super-infection who do not become superinfected may also provide a very interesting avenue for new vaccine research.

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".

HIV superinfection (also called HIV reinfection) is a condition in which a person with an established human immunodeficiency virus infection acquires a second strain of HIV, often of a different subtype. The HIV superinfection strain (a recombinant strain) appears when a person becomes simultaneously infected by two different strains, allowing the two viruses to exchange genetic material, resulting in a new unique strain that can possess the resistances of both previous strains. This new strain co-exists with the two prior strains and may cause more rapid disease progression or carry multiple resistances to certain HIV medications.

People with HIV risk superinfection by the same actions that would place a non-infected person at risk of acquiring HIV. These include sharing needles and forgoing condoms with HIV-positive sexual partners. For many years superinfection was thought to occur mainly in high-risk populations. Research from Uganda published in 2012 indicates that HIV superinfection among HIV-infected individuals within a general population remains unknown. Further research from "The Journal of Infectious Diseases" indicates that there have been 16 documented cases of superinfection since 2002.

When HIV-negative children take isoniazid after they have been exposed to tuberculosis, their risk to contract tuberculosis is reduced. A Cochrane review investigated whether giving isoniazid to HIV-positive children can help to prevent this vulnerable group from getting tuberculosis. They included three trials conducted in South Africa and Botswana and found that isoniazid given to all children diagnosed with HIV may reduce the risk of active tuberculosis and death in children who are not on antiretroviral treatment. For children taking antiretroviral medication, no clear benefit was detected.

Paravaccinia is a member of the Parapoxvirus family. It has a cylindrical body about 140 X 310 nm in size, with convex ends covered in a criss-cross pattern of rope like structures. The virus is resistant to cold, dehydration, and temperatures up to 56 °C. Upon injecting a cell with its genome, the virus begins transcription in the cytoplasm using viral RNA polymerase. As the virus progresses through the cell, the host begins to replicate the viral genome between 140 minutes and 48 hours.

Stress often serves as the final precursor to BRD. The diseases that make up BRD can persist in a cattle herd for a long period of time before becoming symptomatic, but immune systems weakened by stress can stop controlling the disease. Major sources of stress come from the shipping process

and from the co-mingling of cattle.

Weather may be another possible factor. Cases are more common in the fall (although this is the traditional time to sell cattle), and while the relationship between weather and BRD is poorly understood, it is often suggested to avoid transporting cattle during extreme weather.