Brain abscess is most commonly due to direct extension of infection from infected middle ear, mastoid sinus, or paranasal sinuses; traumatic injuries, or infected prostheses. There can also be more distant spread from the lungs or from infected emboli. There is increased incidence in immunosuppressed patients. The most frequent organisms cultured are various streptococci, Bacteroides, gram-negative organisms, and Staphylococcus aureus. Mixed infections are present in 30%-60% of cases. Apparently the CSF findings in brain abscess are not significantly influenced by the causative organism or the location of the lesion. About 10% of patients are said to have normal CSF test results. The remainder usually have a picture compatible with aseptic meningitis. The spinal fluid is most often clear, and about 70% of patients are said to have increased pressure. Protein levels are normal in nearly 25% of patients, in about 55% the values are between 45 and 100 mg/100 ml (0.45-1.0 g/L), and in the remaining 20% the values are more than 100 mg/100 ml. The CSF glucose level is normal. Cell counts are variable; about 30% are between 5 and 25, about 25% are between 25 and 100, and about 25% are between 100 and 500/cu mm. Lymphocytes generally predominate, but a significant percentage (5%-25%) of polymorphonuclear neutrophils are said to be nearly always present. In occasional cases, an abscess breaks through to the subarachnoid space and results in purulent meningitis. CT or MRI is very helpful in demonstrating intracerebral abscesses. Radionuclide brain scans are useful if CT is not available.
Tag: Staphylococcus
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Pneumonia
The word pneumonia means inflammation of the lung. Although this could result from noninfectious sources (e.g., a chemical inflammation secondary to aspiration), the great majority of cases are due to bacterial or nonbacterial infectious agents. Almost any bacterium, many species of fungi, and many viruses could be associated with pneumonia under some circumstances. Except for the newborn, in the early pediatric age group viruses are the most common etiology, followed by Staphylococcus infections. In older children and young adults, viruses still markedly predominate, but pneumonococci become more prevalent. In middle-aged and older adults, pneumococci are the most frequent bacteria and H. influenzae is also important, although viruses still are more frequent numerically. Mycoplasma pneumoniae is a very important cause of pneumonia in older children, young adults, and middle-aged adults but may appear at any age. In debilitated persons, alcoholics, persons with depressed immunologic defenses, and the elderly, pneumococci are still very important, but other bacteria become much more common, especially Staphylococcus and Klebsiella. Staphylococcal pneumonia is particularly likely to occur following a viral pneumonia, such as influenza. Legionella infections are assuming more importance in adults and the elderly, although their true incidence is not known because Legionella is not tested for routinely.
The most important nonbacterial agents producing lung infection are the respiratory-syncytial virus, influenza virus, the Aspergillus fungus, and an organism classified as a parasite, Pneumocystis carinii. Diseases caused by viruses, fungi, and parasites are discussed in other chapters.