Diagnosis of bacterial respiratory tract infections
In HIV patients, bacterial pneumonias develop more frequently and have a more severe course. The leading causative agent is Streptococcus pneumoniae; Haemophilus influenzae and staphylococci are also encountered.
The basic diagnostic algorithm includes:
- Laboratory tests: a complete blood count (CBC) registers a classic nonspecific marker — neutrophilic leukocytosis.
- Radiography: may show both typical focal bronchopneumonia and atypical diffuse infiltration or cavities. It is important to remember that sometimes radiological changes are completely absent.
- Etiological verification: bronchoalveolar lavage (BAL) and blood culture are considered the "gold standard". The material must be collected prior to initiating empiric antibacterial therapy.
If there is no clinical improvement 72 hours after starting first-line therapy, differential diagnosis with tuberculosis and Pneumocystis pneumonia is required.
Laboratory assessment of intestinal infections
The gastrointestinal tract in HIV is frequently affected by salmonellae, shigellae, campylobacter, and Clostridium difficile. The course of such diseases is severe, and in salmonellosis, generalization (septicopyemia) is possible in 5–10% of cases.
The basis of diagnosis relies on two methods:
- Culture (bacteriological): culture of feces, vomit, gastric lavage fluid, and bile. If a systemic form is suspected, blood and bone marrow are additionally examined.
- Serological: application of ELISA and indirect hemagglutination assay (IHA). The key criterion here is not a single positive result, but a reliable increase in antibody titer over time.
Diagnosis of indicator herpetic infection
Infection caused by herpes simplex virus (HSV) is prone to dissemination when immunity is suppressed. The diagnostic workup for suspected herpes includes four main groups of methods:
- Cytomorphological: staining of smears (vesicle fluid, saliva, cerebrospinal fluid) with Romanowsky-Giemsa stain. A pathognomonic sign is the presence of multinucleated giant cells (syncytia) and specific Cowdry cells with intranuclear inclusions.
- Virological: cultivation of the virus on cell lines with evaluation of the cytopathic effect. Changes are noticeable within 24 hours. Identification is performed using monoclonal antibodies (DFA, ELISA).
- Serological: evaluation of paired sera. A 4-fold or greater increase in IgM titer indicates a primary infection. An increase in IgG indicates a recurrent form of the disease.
- Molecular biological: detection of viral genetic material using PCR.
Briefly: answers to topical questions
Which antibacterial drugs belong to the first line for empiric therapy of pneumonia in HIV-infected patients?
First-line drugs for initial monotherapy of bacterial pneumonia in the setting of HIV infection include oral antibiotics from four pharmacological groups.
- Penicillins — amoxicillin, as well as beta-lactamase-inhibitor protected aminopenicillins to overcome flora resistance.
- Macrolides — erythromycin, clarithromycin, and azithromycin (prescribed for penicillin allergy or suspected atypical flora).
- Respiratory fluoroquinolones — drugs possessing antipneumococcal activity.
- Tetracyclines — doxycycline.
This therapy is used predominantly in outpatient treatment or for a mild course of the disease.
Class and exam questions
What to do if first-line antibiotics for pneumonia do not work?
If there is no effect after 72 hours, the patient is hospitalized, switched to second-line drugs, and tuberculosis and pneumocystosis are mandatorily ruled out.
What material is taken for bacterial culture when systemic salmonellosis is suspected?
In addition to feces and vomit, blood and bone marrow are examined to detect generalization of the process.
How to distinguish primary herpes from a relapse using antibodies?
A sharp (4-fold) increase in IgM class antibodies indicates primary infection, whereas an increase in IgG titer is characteristic of a recurrent process.
What else to study on this topic
- Principles of antibacterial therapy for pneumonia: first- and second-line drugs
- Treatment regimens for salmonellosis, shigellosis, and clostridiosis
- Pathogenesis of neurotropism and the mechanism of herpesvirus persistence
- Clinical classification of herpes simplex (genital, ophthalmoherpes)
Master the complete topic in the «Infectious Diseases» course
This is a summary. The course covers everything tested in classes and exams.
- Full study guide on "Diagnosis of HIV Infection" and 3,312 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 41 video lessons on the subject
Other topics in the section "Viral Hepatitis and HIV"
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.