The diagnosis of actinomycosis can be a difficult one to make. In addition to microbiological examinations, magnetic resonance imaging and immunoassays may be helpful.

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 diagnosis is made by an ophthalmologist/optometrist correlating typical history, symptoms and signs. Many times it may be missed and misdiagnosed as bacterial ulcer. A definitive diagnosis is established only after a positive culture report (lactophenol cotton blue, calcoflour medium), typically taking a week, from the corneal scraping. Recent advances have been made in PCR ref 3./immunologic tests which can give a much quicker result.

"Actinomyces" bacteria are generally sensitive to penicillin, which is frequently used to treat actinomycosis. In cases of penicillin allergy, doxycycline is used.

Sulfonamides such as sulfamethoxazole may be used as an alternative regimen at a total daily dosage of 2-4 grams. Response to therapy is slow and may take months.

Hyperbaric oxygen therapy may also be used as an adjunct to conventional therapy when the disease process is refractory to antibiotics and surgical treatment.

Dempster-Shafer Theory is used for detecting skin infection and displaying the result of the detection process.

The most informative test is to scrape the lesion and add potassium hydroxide (KOH), then examine under a microscope. (KOH scrapings are commonly used to examine fungal infections.) The pathognomonic finding is observing medlar bodies, sclerotic cells. Scrapings from the lesion can also be cultured to identify the organism involved. Blood tests and imaging studies are not commonly used.

On histology, chromoblastomycosis manifests as pigmented yeasts resembling "copper pennies". Special stains, such as periodic acid schiff and Gömöri methenamine silver, can be used to demonstrate the fungal organisms if needed.

Diagnosis of mycetoma is usually established clinically in endemic areas.

X rays and ultrasonography may be employed in evaluating the extent of the disease. X rays findings are extremely variable. The disease is most often observed at an advanced stage that exhibits extensive destruction of all bones of the foot. Rarely, a single lesion may be seen in the tibia where the picture is identical with chronic osteomyelitis. Cytology of fine needle aspirate or pus from the lesion, and tissue biopsy may be undertaken sometimes. Some publications have claimed a "dot in a circle sign" as a characteristic MRI feature for this condition (this feature has also been described on ultrasound).

To make a diagnosis of bacterial vaginosis, a swab from inside the vagina should be obtained. These swabs should be tested for:

- A characteristic "fishy" odor on wet mount. This test, called the "whiff test", is performed by adding a small amount of potassium hydroxide to a microscopic slide containing the vaginal discharge. A characteristic fishy odor is considered a positive whiff test and is suggestive of bacterial vaginosis.

- Loss of acidity. To control bacterial growth, the vagina is normally slightly acidic with a pH of 3.8–4.2. A swab of the discharge is put onto litmus paper to check its acidity. A pH greater than 4.5 is considered alkaline and is suggestive of bacterial vaginosis.

- The presence of "clue cells" on wet mount. Similar to the whiff test, the test for clue cells is performed by placing a drop of sodium chloride solution on a slide containing vaginal discharge. If present, clue cells can be visualized under a microscope. They are so-named because they give a clue to the reason behind the discharge. These are epithelial cells that are coated with bacteria.

Two positive results in addition to the discharge itself are enough to diagnose BV. If there is no discharge, then all three criteria are needed.

Differential diagnosis for bacterial vaginosis includes the following:

- Normal vaginal discharge.

- Candidiasis (thrush, or a yeast infection).

- Trichomoniasis, an infection caused by "Trichomonas vaginalis".

- Aerobic vaginitis

The Center For Disease Control (CDC) defines STIs as "a variety of clinical syndromes and infections caused by pathogens that can be acquired and transmitted through sexual activity." But the CDC does not specifically identify BV as sexually transmitted infection.

The following clinical conditions may be considered before diagnosing a patient with mycetoma:

1. Tuberculous ulcer

2. Kaposi's sarcoma, a vascular tumour of skin usually seen in AIDS.

3. Leprosy

4. Syphilis

5. Malignant neoplasm

6. Tropical ulcer

7. Botryomycosis, a skin infection usually caused by the bacteria Staphylococcus aureus.

The Nugent Score is now rarely used by physicians due to the time it takes to read the slides and requires the use of a trained microscopist. A score of 0-10 is generated from combining three other scores. The scores are as follows:

- 0–3 is considered negative for BV

- 4–6 is considered intermediate

- 7+ is considered indicative of BV.

At least 10–20 high power (1000× oil immersion) fields are counted and an average determined.

DNA hybridization testing with Affirm VPIII was compared to the Gram stain using the Nugent criteria. The Affirm VPIII test may be used for the rapid diagnosis of BV in symptomatic women but uses expensive proprietary equipment to read results, and does not detect other pathogens that cause BV, including Prevotella spp, Bacteroides spp, & Mobiluncus spp.

Diagnosis of subacute bacterial endocarditis can be done by collecting three blood culture specimens over a 24-hour period for analysis, also it can usually be indicated by the existence of:

- Osler's nodes

- Roth's spots

- Nail clubbing

Prevention of trauma with vegetable / organic matter, particularly in agricultural workers while harvesting can reduce the incidence of fungal keratitis. Wearing of broad protective glasses with side shields is recommended for people at risk for such injuries.

In chronic bacterial prostatitis there are bacteria in the prostate, but there may be no symptoms or milder symptoms than occur with acute prostatitis. The prostate infection is diagnosed by culturing urine as well as prostate fluid (expressed prostatic secretions or EPS) which are obtained by the doctor performing a rectal exam and putting pressure on the prostate. If no fluid is recovered after this prostatic massage, a post massage urine should also contain any prostatic bacteria.

Prostate specific antigen levels may be elevated, although there is no malignancy. Semen analysis is a useful diagnostic tool. Semen cultures are also performed. Antibiotic sensitivity testing is also done to select the appropriate antibiotic. Other useful markers of infection are seminal elastase and seminal cytokines.

Bumblefoot is so named because of the characteristic "bumbles" or lesions, as well as swelling of the foot pad, symptomatic of an infection. Topical antiseptics in addition to oral or injected antibiotics may be used to combat the infection, which if left untreated may be fatal.

Diagnosis and the imaging (and laboratory) studies to be ordered largely depend on the patient history, signs and symptoms. If a persistent sore throat with signs of sepsis are found, physicians are cautioned to screen for Lemierre's syndrome.

Laboratory investigations reveal signs of a bacterial infection with elevated C-reactive protein, erythrocyte sedimentation rate and white blood cells (notably neutrophils). Platelet count can be low or high. Liver and kidney function tests are often abnormal.

Thrombosis of the internal jugular vein can be displayed with sonography. Thrombi that have developed recently have low echogenicity or echogenicity similar to the flowing blood, and in such cases pressure with the ultrasound probe show a non-compressible jugular vein - a sure sign of thrombosis. Also color or power Doppler ultrasound identify a low echogenicity blood clot. A CT scan or an MRI scan is more sensitive in displaying the thrombus of the intra-thoracic retrosternal veins, but are rarely needed.

Chest X-ray and chest CT may show pleural effusion, nodules, infiltrates, abscesses and cavitations.

Bacterial cultures taken from the blood, joint aspirates or other sites can identify the causative agent of the disease.

Other illnesses that can be included in the differential diagnosis are:

- Q fever

- Tuberculosis

- Pneumonia

When no pus is present, warm soaks for acute paronychia is reasonable, even though there is a lack of evidence to support its use. Antibiotics such as clindamycin or cephalexin are also often used, the first being more effective in areas where MRSA is common. If there are signs of an abscess (the presence of pus) drainage is recommended.

Chronic paronychia is treated by avoiding whatever is causing it, a topical antifungal, and a topical steroid. In those who do not improve following these measures oral antifungals and steroids may be used or the nail fold may be removed surgically.

The standard treatment is with a minimum of four weeks of high-dose intravenous penicillin with an aminoglycoside such as gentamicin.

The use of high-dose antibiotics is largely based upon animal models.

Leo Loewe of Brooklyn Jewish Hospital was the first to successfully treat subacute bacterial endocarditis with penicillin. Loewe reported at the time seven cases of subacute bacterial endocarditis in 1944.

"M. pneumoniae" infections can be differentiated from other types of pneumonia by the relatively slow progression of symptoms. A positive blood test for cold-hemagglutinins in 50–70% of patients after 10 days of infection (cold-hemagglutinin-test should be used with caution or not at all, since 50% of the tests are false-positive), lack of bacteria in a Gram-stained sputum sample, and a lack of growth on blood agar.

PCR has also been used.

In a normal umbilical stump, you first see the umbilicus lose its characteristic bluish-white, moist appearance and become dry and black After several days to weeks, the stump should fall off and leave a pink fleshy wound which continues to heal as it becomes a normal umbilicus.

For an infected umbilical stump, diagnosis is usually made by the clinical appearance of the umbilical cord stump and the findings on history and physical examination. There may be some confusion, however, if a well-appearing neonate simply has some redness around the umbilical stump. In fact, a mild degree is common, as is some bleeding at the stump site with detachment of the umbilical cord. The picture may be clouded even further if caustic agents have been used to clean the stump or if silver nitrate has been used to cauterize granulomata of the umbilical stump.

Diagnosis of FVR is usually by clinical signs, especially corneal ulceration. Definitive diagnosis can be done by direct immunofluorescence or virus isolation. However, many healthy cats are subclinical carriers of feline herpes virus, so a positive test for FHV-1 does not necessarily indicate that signs of an upper respiratory tract infection are due to FVR. Early in the course of the disease, histological analysis of cells from the tonsils, nasal tissue, or nictitating membrane (third eyelid) may show inclusion bodies (a collection of viral particles) within the nucleus of infected cells.

No preventive measure is known aside from avoiding the traumatic inoculation of fungi. At least one study found a correlation between walking barefoot in endemic areas and occurrence of chromoblastomycosis on the foot.

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.

Vulvovaginitis in children may be "nonspecific", or caused by irritation with no known infectious cause, or infectious, caused by a pathogenic organism. Nonspecific vulvovaginitis may be triggered by fecal contamination, sexual abuse, chronic diseases, foreign bodies, nonestrogenized epithelium, chemical irritants, eczema, seborrhea, or immunodeficiency. It is treated with topical steroids; antibiotics may be given in cases where itching has resulted in a secondary infection.

Infectious vulvovaginitis can be caused by group A beta-hemolytic "Streptococcus" (7-20% of cases), "Haemophilus influenzae, Streptococcus pneumoniae, Staphylococcus aureus, Shigella, Yersinia", or common STI organisms ("Neisseria gonorrhoeae, Chlamydia trachomatis, Trichomonas vaginalis", herpes simplex virus, and human papillomavirus)"." Symptoms and treatment of infectious vulvovaginitis vary depending on the organism causing it. "Shigella" infections of the reproductive tract usually coexist with infectious of the gastrointestinal tract and cause mucous, purulent discharge. They are treated with trimethoprim-sulfamethoxazole. "Streptococcus" infections cause similar symptoms to nonspecific vulvovaginitis and are treated with amoxicillin. STI-associated vulvovaginitis may be caused by sexual abuse or vertical transmission, and are treated and diagnosed like adult infections.

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.

As the infection is usually transmitted into humans through animal bites, antibiotics usually treat the infection, but medical attention should be sought if the wound is severely swelling. Pasteurellosis is usually treated with high-dose penicillin if severe. Either tetracycline or chloramphenicol provides an alternative in beta-lactam-intolerant patients. However, it is most important to treat the wound.