Diagnosis can be achieved through blood cultures, or cultures of other bodily fluids such as sputum. Bone marrow culture can often yield an earlier diagnosis, but is usually avoided as an initial diagnostic step because of its invasiveness.

Many people will have anemia and neutropenia if bone marrow is involved. MAC bacteria should always be considered in a person with HIV infection presenting with diarrhea.

The diagnosis requires consistent symptoms with two additional signs:

- Chest X-ray or CT scan showing evidence of right middle lobe (or left lingular lobe) lung infection

- Sputum culture or bronchoalveolar lavage culture demonstrating the infection is caused by MAC

Disseminated MAC is most readily diagnosed by one positive blood culture. Blood cultures should be performed in patients with symptoms, signs, or laboratory abnormalities compatible with mycobacterium infection. Blood cultures are not routinely recommended for asymptomatic persons, even for those who have CD4+ T-lymphocyte counts less than 100 cells/uL.

Patients with symptoms of CAP require evaluation. Diagnosis of pneumonia is made clinically, rather than on the basis of a particular test. Evaluation begins with a physical examination by a health provider, which may reveal fever, an increased respiratory rate (tachypnea), low blood pressure (hypotension), a fast heart rate (tachycardia) and changes in the amount of oxygen in the blood. Palpating the chest as it expands and tapping the chest wall (percussion) to identify dull, non-resonant areas can identify stiffness and fluid, signs of CAP. Listening to the lungs with a stethoscope (auscultation) can also reveal signs associated with CAP. A lack of normal breath sounds or the presence of crackles can indicate fluid consolidation. Increased vibration of the chest when speaking, known as tactile fremitus, and increased volume of whispered speech during auscultation can also indicate fluid.

When signs of pneumonia are discovered during evaluation, chest X-rays, are performed to support a diagnosis of CAP, and examination of the blood and sputum for infectious microorganisms and blood tests may be used to support a diagnosis of CAP. Diagnostic tools depend on the severity of illness, local practices and concern about complications of the infection. All patients with CAP should have their blood oxygen monitored with pulse oximetry. In some cases, arterial blood gas analysis may be required to determine the amount of oxygen in the blood. A complete blood count (CBC) may reveal extra white blood cells, indicating infection.

Chest X-rays and X-ray computed tomography (CT) can reveal areas of opacity (seen as white), indicating consolidation. CAP does not always appear on x-rays, because the disease is in its initial stages or involves a part of the lung an x-ray does not see well. In some cases, chest CT can reveal pneumonia not seen on x-rays. However, congestive heart failure or other types of lung damage can mimic CAP on x-rays.

Several tests can identify the cause of CAP. Blood cultures can isolate bacteria or fungi in the bloodstream. Sputum Gram staining and culture can also reveal the causative microorganism. In severe cases, bronchoscopy can collect fluid for culture. Special tests can be performed if an uncommon microorganism is suspected, such as urinalysis for Legionella antigen in Legionnaires' 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.

MAC in patients with HIV disease is theorized to represent recent acquisition rather than latent infection reactivating (which is the case in many other opportunistic infections in immunocompromised patients).

The risk of MAC is inversely related to the patient's CD4 count, and increases significantly when the CD4 count decreases below 50 cells/mm³. Other risk factors for acquisition of MAC infection include using an indoor swimming pool, consumption of raw or partially cooked fish or shellfish, bronchoscopy and treatment with granulocyte stimulating factor.

Disseminated disease was previously the common presentation prior to the advent of highly active antiretroviral therapy (HAART). Today, in regions where HAART is the standard of care, localized disease presentation is more likely. This generally includes a focal lymphadenopathy/lymphadenitis.

"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.

Some CAP patients require intensive care, with clinical prediction rules such as the pneumonia severity index and CURB-65 guiding the decision to hospitalize. Factors increasing the need for hospitalization include:

- Age greater than 65

- Underlying chronic illnesses

- Respiratory rate greater than 30 per minute

- Systolic blood pressure less than 90 mmHg

- Heart rate greater than 125 per minute

- Temperature below 35 or over 40 °C

- Confusion

- Evidence of infection outside the lung

Laboratory results indicating hospitalization include:

- Arterial oxygen tension less than 60 mm Hg

- Carbon dioxide over 50 mmHg or pH under 7.35 while breathing room air

- Hematocrit under 30 percent

- Creatinine over 1.2 mg/dl or blood urea nitrogen over 20 mg/dl

- White-blood-cell count under 4 × 10^9/L or over 30 × 10^9/L

- Neutrophil count under 1 x 10^9/L

X-ray findings indicating hospitalization include:

- Involvement of more than one lobe of the lung

- Presence of a cavity

- Pleural effusion

It is currently recommended that HIV-infected individuals with TB receive combined treatment for both diseases, irrespective of CD4+ cell count. ART (Anti Retroviral Therapy) along with ATT (Anti Tuberculosis Treatment) is the only available treatment in present time. Though the timing of starting ART is the debatable question due to the risk of immune reconstitution inflammatory syndrome (IRIS). The advantages of early ART include reduction in early mortality, reduction in relapses, preventing drug resistance to ATT and reduction in occurrence of HIV-associated infections other than TB. The disadvantages include cumulative toxicity of ART and ATT, drug interactions leading to inflammatory reactions are the limiting factors for choosing the combination of ATT and ART.

A systematic review investigated the optimal timing of starting antiretroviral therapy in adults with newly diagnosed pulmonary tuberculosis. The review authors included eight trials, that were generally well-conducted, with over 4500 patients in total. The early provision of antiretroviral therapy in HIV-infected adults with newly diagnosed tuberculosis improved survival in patients who had a low CD4 count (less than 0.050 x 109 cells/L). However, such therapy doubled the risk for IRIS. Regarding patients with higher CD4 counts (more than 0.050 x 109 cells/L), the evidence is not sufficient to make a conclusion about benefits or risks of early antiretroviral therapy.

While antibiotics with activity specifically against "M. pneumoniae" are often used (e.g., erythromycin, doxycycline), it is unclear if these result in greater benefit than using antibiotics without specific activity against this organism in those with an infection acquired in the community.

The specific criteria for diagnosis of CPA are:

Chest X-rays showing one or more lung cavities. There may be a fungal ball present or not.

Symptoms lasting more than 3 months, usually including weight loss, fatigue, cough, coughing blood (haemoptysis) and breathlessness

A blood test or tissue fluid test positive for Aspergillus species

Aspergilloma

An aspergilloma is a fungal mass caused by a fungal infection with Aspergillus species that grows in either scarred lungs or in a pre-existing lung cavity, which may have been caused by a previous infection. Patients with a previous history of tuberculosis, sarcoidosis, cystic fibrosis or other lung disease are most susceptible to an aspergilloma. Aspergillomas may have no specific symptoms but in many patients there is some coughing up of blood called haemoptysis - this may be infrequent and in small quantity, but can be severe and then it requires urgent medical help.

Tests used to diagnose an aspergilloma may include:

- Chest X-ray

- Chest CT

- Sputum culture

- Bronchoscopy or bronchoscopy with lavage (BAL)

- Serum precipitins for aspergillus (blood test to detect antibodies to aspergillus)

Almost all aspergillomas are caused by "Aspergillus fumigatus". In diabetic patients it may be caused by "Aspergillus niger". It is very rarely caused by "Aspergillus flavus", "Aspergillus oryzae", "Aspergillus terreus" or "Aspergillus nidulans".

Successful diagnosis of XDR-TB depends on the patient’s access to quality health-care services. If TB bacteria are found in the sputum, the diagnosis of TB can be made in a day or two, but this finding will not be able to distinguish between drug-susceptible and drug-resistant TB. To evaluate drug susceptibility, the bacteria need to be cultivated and tested in a suitable laboratory. Final diagnosis in this way for TB, and especially for XDR-TB, may take from 6 to 16 weeks. To reduce the time needed for diagnosis, new tools for rapid TB diagnosis are urgently needed.

The original method used to test for MDR-TB and XDR-TB was the Drug Susceptibility Testing (DST). DST is capable of determining how well four primary antitubercular drugs inhibit the growth of Mycobacterium Tuberculosis. The four primary antitubercular drugs are Isoniazid, Rifampin, Ethambutol and Pyrazinamide. Drug Susceptibility testing is done by making a Lowenstein-Jensen medium plate and spreading the bacteria on the plate. Disks containing one of the four primary drugs are added to the plate. After weeks of allowing the bacteria to grow the plate is checked for clear areas around the disk. If there is a clear area, the drug has killed the bacteria and most likely the bacteria is not resistant to that drug.

As "Mycobacterium tuberculosis" evolved new strains of resistant bacteria were being found such as XDR-TB. The problem was that primary DST was not suitable for testing bacteria strains that were extensively drug resistant. This problem was starting to be fixed when drug susceptibility tests started including not just the four primary drugs, but secondary drugs. This secondary test is known as Bactec MGIT 960 System. Although Bactec MGIT 960 System was accurate it was still slow at determining the level of resistance.

Diagnosis of MDR and XDR-TB in children is challenging. With an increasing number of cases being reported worldwide there is a great need for better diagnostic tools available for pediatric patients.

In recent years drug resistant tuberculosis testing has shown a lot of progress. Some studies have found an in-house assay that could rapidly detect resistance to drugs involved in the definition of XDR-TB directly from smear-positive specimens. The assay is called Reverse Line Blot Hybridization Assay also known as RLBH. The study showed that the results of RLBH were as accurate as other drug susceptibility tests, but at the same time didn`t take weeks to get results. RLBH testing only took 3 days to determine how resistant the strain of bacteria was.

The current research has shown progress in the testing of drug resistance. A recent study found that a research technique known as direct nitrate reductase assay (D-NRA) showed efficient accuracy for the rapid and simultaneous detection of resistance to isoniazid (INH), rifampicin (RIF), kanamycin (KAN) and ofloxacin (OFL). D-NRA results were obtained in 16.9 days, comparably less than other drug susceptibility testing. At the same time the study mentioned how D-NRA is a low-cost technology, easy to set up in clinical laboratories and suitable to be used for DST of M. tuberculosis in all smear-positive samples.

Vaccination helps prevent bronchopneumonia, mostly against influenza viruses, adenoviruses, measles, rubella, streptococcus pneumoniae, haemophilus influenzae, diphtheria, bacillus anthracis, chickenpox, and bordetella pertussis.

Chest radiographs (X-ray photographs) often show a pulmonary infection before physical signs of atypical pneumonia are observable at all.

This is occult pneumonia. In general, occult pneumonia is rather often present in patients with pneumonia and can also be caused by "Streptococcus pneumoniae", as the decrease of occult pneumonia after vaccination of children with a pneumococcal vaccine suggests.

Infiltration commonly begins in the perihilar region (where the bronchus begins) and spreads in a wedge- or fan-shaped fashion toward the periphery of the lung field. The process most often involves the lower lobe, but may affect any lobe or combination of lobes.

Antibiotics do not help the many lower respiratory infections which are caused by parasites or viruses. While acute bronchitis often does not require antibiotic therapy, antibiotics can be given to patients with acute exacerbations of chronic bronchitis. The indications for treatment are increased dyspnoea, and an increase in the volume or purulence of the sputum. The treatment of bacterial pneumonia is selected by considering the age of the patient, the severity of the illness and the presence of underlying disease. Amoxicillin and doxycycline are suitable for many of the lower respiratory tract infections seen in general practice.

Gram-positive, nonmotile and acid-fast rods (1-3 µm x 0.2-0.4 µm). Sometimes long rods with occasional beaded or swollen cells having non-acid-fast ovoid bodies at one end.

Colony characteristics

- Smooth hemispheric colonies, usually off-white or cream colored. May be butyrous, waxy, multilobate and even rosette clustered (dilute inocula).

- On Malachite green containing media, such as Löwenstein-Jensen media, colonies can absorb the green dye.

Physiology

- Rapid growth on Löwenstein-Jensen media within 2–4 days.

- No growth at 45 °C, but grows on MacConkey agar.

Differential characteristics

- Differentiation from "M. fortuitum subsp. acetamidolyticum" by its ability to use L-glutamate and its inability to use acetamide as simultaneous nitrogen and carbon source. Both subspecies share an identical 5'-16S rDNA sequence. However, the ITS sequences are different.

The 2007 guideline “Official American Thoracic Society (ATS) and Infectious Diseases Society of America (IDSA) statement: diagnosis, treatment, and prevention of non-tuberculosis mycobacterial diseases”, notes that M. fortuitum isolates are usually susceptible to multiple oral antimicrobial agents, including the macrolides and quinolones, doxycycline and minocycline, and sulfonamides. Isolates of this mycobacterium are susceptible to the beta-lactam antibiotics, belonging to the carbopenam subgroup, such as Imipenem. Imipenem is a broad spectrum antibiotic produced by the bacteria Streptomyces cattleya. Ondansetron HCL (Zofran) is an antiemetic often given to offset the nausea and vomiting that are a common side effect of Imipenem. Severe infections require IV treatment combined with oral antibiotics for a prolonged period, up to several months. The guideline recommends “for serious skin, bone, and soft tissue M fortuitum disease, a minimum of 4 months of therapy with at least two agents with in vitro activity against the clinical isolate is necessary to provide a high likelihood of cure. Surgery is generally indicated with extensive disease, abscess formation, or where drug therapy is difficult.”

The Mantoux tuberculin skin test is often used to screen people at high risk for TB. Those who have been previously immunized may have a false-positive test result. The test may be falsely negative in those with sarcoidosis, Hodgkin's lymphoma, malnutrition, and most notably, active tuberculosis. Interferon gamma release assays, on a blood sample, are recommended in those who are positive to the Mantoux test. These are not affected by immunization or most environmental mycobacteria, so they generate fewer false-positive results. However, they are affected by "M. szulgai", "M. marinum", and "M. kansasii". IGRAs may increase sensitivity when used in addition to the skin test, but may be less sensitive than the skin test when used alone.

Countries aim to prevent XDR-TB by ensuring that the work of their national TB control programmes, and of all practitioners working with people with TB, is carried out according to the International Standards for TB Care. These emphasize providing proper diagnosis and treatment to all TB patients, including those with drug-resistant TB; assuring regular, timely supplies of all anti-TB drugs; proper management of anti-TB drugs and providing support to patients to maximize adherence to prescribed regimens; caring for XDR-TB cases in a centre with proper ventilation, and minimizing contact with other patients, particularly those with HIV, especially in the early stages before treatment has had a chance to reduce the infectiousness. Also an effective disease control infrastructure is necessary for the prevention of XDR tuberculosis. Increased funding for research, and strengthened laboratory facilities are much required. Immediate detection through drug susceptibility testing's are vital, when trying to stop the spread of XDR tuberculosis.

Diagnosing active tuberculosis based only on signs and symptoms is difficult, as is diagnosing the disease in those who are immunosuppressed. A diagnosis of TB should, however, be considered in those with signs of lung disease or constitutional symptoms lasting longer than two weeks. A chest X-ray and multiple sputum cultures for acid-fast bacilli are typically part of the initial evaluation. Interferon-γ release assays and tuberculin skin tests are of little use in the developing world. Interferon gamma release assays (IGRA) have similar limitations in those with HIV.

A definitive diagnosis of TB is made by identifying "M. tuberculosis" in a clinical sample (e.g., sputum, pus, or a tissue biopsy). However, the difficult culture process for this slow-growing organism can take two to six weeks for blood or sputum culture. Thus, treatment is often begun before cultures are confirmed.

Nucleic acid amplification tests and adenosine deaminase testing may allow rapid diagnosis of TB. These tests, however, are not routinely recommended, as they rarely alter how a person is treated. Blood tests to detect antibodies are not specific or sensitive, so they are not recommended.

Initial diagnosis may be via symptoms, but is usually confirmed via an antigen and antibody test. A PCR-based test is also available. Although any of these tests can confirm psittacosis, false negatives are possible and so a combination of clinical and lab tests is recommended before giving the bird a clean bill of health. It may die within three weeks.

Antibiotics are the treatment of choice for bacterial pneumonia, with ventilation (oxygen supplement) as supportive therapy. The antibiotic choice depends on the nature of the pneumonia, the microorganisms most commonly causing pneumonia in the geographical region, and the immune status and underlying health of the individual. In the United Kingdom, amoxicillin is used as first-line therapy in the vast majority of patients acquiring pneumonia in the community, sometimes with added clarithromycin. In North America, where the "atypical" forms of community-acquired pneumonia are becoming more common, clarithromycin, azithromycin, or fluoroquinolones as single therapy have displaced the amoxicillin as first-line therapy.

Local patterns of antibiotic-resistance always need to be considered when initiating pharmacotherapy. In hospitalized individuals or those with immune deficiencies, local guidelines determine the selection of antibiotics.

People who have difficulty breathing due to pneumonia may require extra oxygen. An extremely sick individual may require artificial ventilation and intensive care as life-saving measures while his or her immune system fights off the infectious cause with the help of antibiotics and other drugs.

Mycoplasma is found more often in younger than in older people.

Older people are more often infected by Legionella.

Blood analysis shows leukopenia, thrombocytopenia and moderately elevated liver enzymes. Differential diagnosis must be made with typhus, typhoid and atypical pneumonia by Mycoplasma, Legionella or Q fever. Exposure history is paramount to diagnosis.

Diagnosis involves microbiological cultures from respiratory secretions of patients or serologically with a fourfold or greater increase in antibody titers against "C. psittaci" in blood samples combined with the probable course of the disease. Typical inclusions called "Leventhal-Cole-Lillie bodies" can be seen within macrophages in BAL (bronchoalveolar lavage) fluid. Culture of "C. psittaci" is hazardous and should only be carried out in biosafety laboratories.

For some types of chILD and few forms adult ILD genetic causes have been identified. These may be identified by blood tests. For a limited number of cases this is a definite advantage, as a precise molecular diagnosis can be done; frequently then there is no need for a lung biopsy. Testing is available for

Patients with single aspergillomas generally do well with surgery to remove the aspergilloma, and are best given pre-and post-operative antifungal drugs. Often, no treatment is necessary. However, if a patient coughs up blood (haemoptysis), treatment may be required (usually angiography and embolisation, surgery or taking tranexamic acid). Angiography (injection of dye into the blood vessels) may be used to find the site of bleeding which may be stopped by shooting tiny pellets into the bleeding vessel.

For chronic cavitary pulmonary aspergillosis and chronic fibrosing pulmonary aspergillosis, lifelong use of antifungal drugs is usual. Itraconazole and voriconazole are first and second-line anti fungal agents respectively. Posaconazole can be used as third-line agent, for patients who are intolerant of or developed resistance to the first and second-line agents. Regular chest X-rays, serological and mycological parameters as well as quality of life questionnaires are used to monitor treatment progress. It is important to monitor the blood levels of antifungals to ensure optimal dosing as individuals vary in their absorption levels of these drugs.