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

For those with a history of intravenous drug use, an X-ray is recommended before treatment to verify that no needle fragments are present. In this population if there is also a fever present infectious endocarditis should be considered.

The diagnosis is established by a computed tomography (CT) (with contrast) examination. At the initial phase of the inflammation (which is referred to as cerebritis), the immature lesion does not have a capsule and it may be difficult to distinguish it from other space-occupying lesions or infarcts of the brain. Within 4–5 days the inflammation and the concomitant dead brain tissue are surrounded with a capsule, which gives the lesion the famous ring-enhancing lesion appearance on CT examination with contrast (since intravenously applied contrast material can not pass through the capsule, it is collected around the lesion and looks as a ring surrounding the relatively dark lesion). Lumbar puncture procedure, which is performed in many infectious disorders of the central nervous system is contraindicated in this condition (as it is in all space-occupying lesions of the brain) because removing a certain portion of the cerebrospinal fluid may alter the concrete intracranial pressure balances and causes the brain tissue to move across structures within the skull (brain herniation).

Ring enhancement may also be observed in cerebral hemorrhages (bleeding) and some brain tumors. However, in the presence of the rapidly progressive course with fever, focal neurologic findings (hemiparesis, aphasia etc.) and signs of increased intracranial pressure, the most likely diagnosis should be the brain abscess.

Abscesses should be differentiated from empyemas, which are accumulations of pus in a preexisting rather than a newly formed anatomical cavity.

Other conditions that can cause similar symptoms include: cellulitis, a sebaceous cyst and necrotising fasciitis. Cellulitis typically also has an erythematous reaction, but does not confer any purulent drainage.

Diagnosis is by a swab of the affected area for laboratory testing. A Gram stain is performed to show Gram-positive cocci in chains. Then, the organism is cultured on blood agar with an added bacitracin antibiotic disk to show beta-hemolytic colonies and sensitivity (zone of inhibition around the disk) for the antibiotic. Culture on agar not containing blood, and then performing the catalase test should show a negative reaction for all streptococci. "S. pyogenes" is CAMP and hippurate tests negative. Serological identification of the organism involves testing for the presence of group-A-specific polysaccharide in the bacterium's cell wall using the Phadebact test.

The rapid pyrrolidonyl arylamidase (PYR) test is used for the presumptive identification of group A beta-hemolytic streptococci. GBS gives a negative finding on this test.

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.

In some cases, abscesses may be prevented by draining an existing pseudocyst which is likely to become inflamed. However, in most cases the developing of abscesses cannot be prevented.

Most patients who develop pancreatic abscesses have had pancreatitis, so a complete medical history is required as a first step in diagnosing abscesses. On the other hand, a white blood cell count is the only laboratory test that may indicate the presence of an abscess.

Some of the imaging tests are more commonly used to diagnose this condition. Abdominal CT scans, MRIs and ultrasounds are helpful in providing clear images of the inside of the abdomen and successfully used in the diagnosing process. These tests may reveal the presence of infected necrosis which has not yet developed into an abscess and as a result, doctors usually order repeated imaging tests in patients with acute pancreatitis whose abdominal pain worsens and who develop signs of abdominal obstruction. Also, it is recommended that patients who have a prolonged clinical response are tested repeatedly as a prevention method to avoid the development of an abscess that may rupture.

Death occurs in about 10% of cases and people do well about 70% of the time. This is a large improvement from the 1960s due to improved ability to image the head, better neurosurgery and better antibiotics.

The diagnosis usually is made serologically (through complement fixation) and by exclusion of other causes of inguinal lymphadenopathy or genital ulcers. Serologic testing has a sensitivity of 80% after 2 weeks. Serologic testing may not be specific for serotype (has some cross reactivity with other chlamydia species) and can suggest LGV from other forms because of their difference in dilution, 1:64 more likely to be LGV and lower than 1:16 is likely to be other chlamydia forms (emedicine).

For identification of serotypes, culture is often used. Culture is difficult. Requiring a special medium, cycloheximide-treated McCoy or HeLa cells, and yields are still only 30-50%. DFA, or direct fluorescent antibody test, PCR of likely infected areas and pus, are also sometimes used. DFA test for the L-type serovar of C trachomatis is the most sensitive and specific test, but is not readily available.

If polymerase chain reaction (PCR) tests on infected material are positive, subsequent restriction endonuclease pattern analysis of the amplified outer membrane protein A gene can be done to determine the genotype.

Recently a fast realtime PCR (TaqMan analysis) has been developed to diagnose LGV. With this method an accurate diagnosis is feasible within a day. It has been noted that one type of testing may not be thorough enough.

Diagnosis is usually apparent on MRI although plain X-rays and CT examinations can be suggestive. The MRI will reveal air changes in the disc and possibly even external involvement involving the bone or epidural regions. A biopsy may be performed and helps with diagnosis in some cases but often an organism is not obtained. C-reactive protein levels and ESR levels will be elevated and are useful for treatment. Often, the white blood cell count will be normal and the patient will be afebrile.

Aseptic meningitis, or sterile meningitis, is a condition in which the layers lining the brain, the meninges, become inflamed and a pyogenic bacterial source is not to blame. Meningitis is diagnosed on a history of characteristic symptoms and certain examination findings (e.g., Kernig's sign). Investigations should show an increase in the number of leukocytes present in the cerebrospinal fluid (CSF) obtained via lumbar puncture (normally being fewer than five visible leukocytes per microscopic high-power field).

The term "aseptic" is frequently a misnomer, implying a lack of infection. On the contrary, many cases of aseptic meningitis represent infection with viruses or mycobacteria that cannot be detected with routine methods. While the advent of polymerase chain reaction has increased the ability of clinicians to detect viruses such as enterovirus, cytomegalovirus, and herpes virus in the CSF, many viruses can still escape detection. Additionally, mycobacteria frequently require special stains and culture methods that make their detection difficult. When CSF findings are consistent with meningitis, and microbiologic testing is unrevealing, clinicians typically assign the diagnosis of aseptic meningitis—making it a relative diagnosis of exclusion.

Aseptic meningitis can result from non-infectious causes as well. it can be a relatively infrequent side effect of medications, or be a result of an autoimmune disease. There is no formal classification system of aseptic meningitis except to state the underlying cause, if known. The absence of bacteria found in the spinal fluid upon spinal tap, either through microscopic examination or by culture, usually differentiates aseptic meningitis from its pyogenic counterpart.

"Aseptic meningitis", like non-gonococcal urethritis, non-Hodgkin lymphoma and atypical pneumonia, merely states what the condition is not, rather than what it is. Terms such as viral meningitis, bacterial meningitis, fungal meningitis, neoplastic meningitis and drug-induced aseptic meningitis can provide more information about the condition, and without using one of these more specific terms, it is difficult to describe treatment options or prognosis.

Prognosis is highly variable. Spontaneous remission is common. Complete cure can be obtained with proper antibiotic treatments to kill the causative bacteria, such as tetracycline, doxycycline, or erythromycin. Prognosis is more favorable with early treatment. Bacterial superinfections may complicate course. Death can occur from bowel obstruction or perforation, and follicular conjunctivitis due to autoinoculation of infectious discharge can occur.

Diagnosis of anorectal abscess begins with a medical history and physical exam. Imaging studies which can help determine the diagnosis in cases of a deep non-palpable perirectal abscess include pelvic CT scan, MRI or trans-rectal ultrasound. These studies are not necessary, though, in cases which the diagnosis can be made upon physical exam.

"S. pyogenes" infections are best prevented through effective hand hygiene. No vaccines are currently available to protect against "S. pyogenes" infection, although research has been conducted into the development of one. Difficulties in developing a vaccine include the wide variety of strains of "S. pyogenes" present in the environment and the large amount of time and number of people that will be needed for appropriate trials for safety and efficacy of the vaccine.

The diagnosis of viral meningitis is made by clinical history, physical exam, and several diagnostic tests. Most importantly, cerebrospinal fluid (CSF) is collected via lumbar puncture (also known as spinal tap). This fluid, which normally surrounds the brain and spinal cord, is then analyzed for signs of infection. CSF findings that suggest a viral cause of meningitis include an elevated white blood cell count (usually 10-100 cells/µL) with a lymphocytic predominance in combination with a normal glucose level. Increasingly, cerebrospinal fluid PCR tests have become especially useful for diagnosing viral meningitis, with an estimated sensitivity of 95-100%. Additionally, samples from the stool, urine, blood and throat can also help to identify viral meningitis.

In certain cases, a CT scan of the head should be done before a lumbar puncture such as in those with poor immune function or those with increased intracranial pressure.

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

Raised inflammatory markers (high ESR, CRP) are common but nonspecific. Examination of the coughed up mucus is important in any lung infection and often reveals mixed bacterial flora. Transtracheal or transbronchial (via bronchoscopy) aspirates can also be cultured. Fiber optic bronchoscopy is often performed to exclude obstructive lesion; it also helps in bronchial drainage of pus.

Treatment usually includes antibiotics, and reducing the mobility of the affected region, either with a back brace or a plaster cast. Without treatment, the patient may form an abscess which may need to be surgically corrected. Due to the poor vascularity of the disc, drugs required for treatment often include potent agents such as Ciprofloxacin along with Vancomycin. Occasionally, oral drugs can be used to treat the infection but it may fail and IV drugs may be required.

If the patient is an adult many surgeons and doctors now recommend moving little and often and within the pain limits of the medication. Discs respond to osmotic pressure therefore movement is beneficial to increase their blood flow and fluid dynamics. This is why disc patients are no longer told to bed rest. In children whether to bed rest or move a little is decided on an individual basis, depending on the site and severity of the discitis.

Animal pathogens exist as facultative parasites. They are an exceptionally rare cause of meningoencephalitis.

clinical diagnosis include recurrent or recent herpes infection fever, headache, mental symptom, convulsion, disturbance of consciousness, focal signs.

CSF ,EEG, CT, MRI are responsive to specific antivirus agent.

Definite diagnosis – besides the above, the followings are needed

CSF: HSV－antigen,HSV－Antibody, brain biopsy or pathology: Cowdry in intranuclear

CSF: the DNA of the HSV(PCR)

cerebral tissue or specimen of the CSF:HSV

except other viral encephalitis

Anal abscesses are rarely treated with a simple course of antibiotics. In almost all cases surgery will need to take place to remove the abscess. Treatment is possible in an emergency room under local anesthesia, but it is highly preferred to be formally admitted to a hospital and to have the surgery performed in an operating room under general anesthesia.

Generally speaking, a fairly small but deep incision is performed close to the root of the abscess. The surgeon will allow the abscess to drain its exudate and attempt to discover any other related lesions in the area. This is one of the most basic types of surgery, and is usually performed in less than thirty minutes by the anal surgical team. Generally, a portion of the exudate is sent for microbiological analysis to determine the type of infecting bacteria. The incision is not closed (stitched), as the damaged tissues must heal from the inside toward the skin over a period of time.

The affected individual is often sent home within twenty-four hours of the surgery, and may be instructed to perform several 'sitz baths' per day, whereby a small basin (which usually fits over a toilet) is filled with warm water (and possibly, salts) and the affected area is soaked for a period of time. Another method of recovery involves the use of surgical packing, which is initially inserted by the surgical team, with redressing generally performed by hospital staff or a District Nurse (however, following the results of several double-blind studies, the effectiveness of surgical packing has come into question). During the week following the surgery, many patients will have some form of antibiotic therapy, along with some form of pain management therapy, consistent with the nature of the abscess.

The patient usually experiences an almost complete relief of the severe pain associated to his/her abscess upon waking from anesthesia; the pain associated with the opening and draining incision during the post-operative period is often mild in comparison.

The abscesses within the muscle must be drained surgically (not all patient require surgery if there is no abscess). Antibiotics are given for a minimum of three weeks to clear the infection.

Risk factors have been identified which indicate what women will be more likely to develop TOA. These are: increased age, IUD insertion, chlamydia infection, and increased levels of certain proteins (CRP and CA-125) and will alert clinicians to follow up on unresolved symptoms of PID.

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".

Laparoscopy and other imaging tools can visualize the abscess. Physicians are able to make the diagnosis if the abscess ruptures when the woman begins to have lower abdominal pain that then begins to spread. The symptoms then become the same as the symptoms for peritonitis. Sepsis, occurs if left untreated. Ultrasonography is a sensitive enough imaging tool that it can accurately differentiate between pregnancy, hemorrhagic ovarian cysts, endometriosis, ovarian torsion, and tubo-ovarian abscess. Its availability, the relative advancement in the training of its use, its low cost, and because it does not expose the woman (or fetus) to ionizing radiation, ultrasonography an ideal imaging procedure for women of reproductive age.