Central Nervous System Overview

Central Nervous System

• The central nervous system includes the brain and spinal cord, meninges, and sterile environment

• Cerebrospinal fluid (CSF) bathes the brain and spinal cord and is clear and colorless

• CSF is tested for culture, cell counts, glucose, and protein levels

• Meningitis is an inflammation of the meninges

• Purulent meningitis is also known as pyogenic meningitis and usually caused by bacteria

• Aseptic meningitis is typically caused by a virus

• Encephalitis is an inflammation of the brain, often caused by a virus

• Meningoencephalitis is the inflammation of both the brain and meninges

• Routes of infection include hematogenous (most common), where the bloodstream carries organisms to the meninges from a colonized or infected site, or contiguous spread, where an organism spreads from an infected adjacent site such as sinusitis

• Trauma causes a breach of the CNS's protective barrier, with skull fractures being a notable example

• Surgical procedures can introduce microbial contamination and shunts used to remove fluids can also be portals of entry

• Acute bacterial meningitis symptoms might include flu-like symptoms, headache, fever, nausea, vomiting, nuchal rigidity (stiff neck), and photophobia (sensitivity to light). Mental status changes can also occur

• Causative agents for meningitis include E. coli, other gram-negative rods (Klebsiella, Enterobacter), S. agalactiae, Listeria monocytogenes, H. influenzae b, N. meningitidis (meningococci), and S. pneumoniae (pneumococci). Different age groups are more susceptible to different bacteria

• Specimen collection involves lumbar puncture, where a spinal needle is inserted between the 3rd and 4th lumbar vertebrae to obtain CSF

• CSF specimens are transported at room temperature (RT) within 15 minutes of collection for STAT processing and may be stored in incubators or at room temperature

• 3-4 tubes are collected for CSF analysis. Tube #1 is for chemistry (protein and glucose); Tube #2 is for microbiology (gram stain and culture); and Tube #3 is for hematology (cell count and differential).

• Microbiology processing may involve centrifuging the CSF if >1 mL to obtain a sediment for smears and culture. Gram stain smear sensitivity varies from 75% to 90%

• Common culture media include BAP (blood agar plate) and CHOC (chocolate agar), while MAC or EMB may be used if Gram-negative rods are present in the smears. Anaerobic bacteria are sometimes isolated, and incubation is typically performed at 35-37°C in the presence of CO2

• Antigen detection tests help identify group B streptococci, Haemophilus influenzae type b, meningococci, and pneumococci. These tests supplement smear and culture analysis

• Other meningitis types include those caused by Treponema pallidum (syphilis), Borrelia burgdorferi (Lyme), viruses, M. tuberculosis, and fungi

• CSF findings vary depending on the causative organism, with bacteria often associated with neutrophils and viruses with lymphocytes in the CSF fluid.

• Brain abscesses are caused by various organisms, including anaerobic bacteria, staphylococci, viridans and other streptococci. The material is transported and examined in anaerobic conditions and cultured aerobically and anaerobically.

• Encephalitis/Meningoencephalitis is primarily caused by viruses but sometimes by Listeria monocytogenes, rickettsia, mycoplasma, Borrelia burgdorferi

• Parasites like Naegleria and Acanthamoeba can also cause encephalitis.

• Reporting of results for critical values should include immediate notification, ideally, followed by a written report after verbal communication

Body Fluids

• Fluid types include pleural fluid (surrounds lungs), peritoneal fluid (abdominal cavity), pericardial fluid (heart space), synovial fluid (joint fluids), and amniotic fluid (surrounding fetus) - all considered sterile

• Thoracentesis is a procedure to collect pleural fluid from the pleural cavity, which is the space between the lungs and the chest wall.

• Pleural effusion signifies excess pleural fluid.

• Empyema involves infection spreading from the lungs, resulting in purulent (pus-filled) pleural fluid. Bacteria recovered from the pleural fluid often cause pneumonia.

• Paracentesis is a procedure for collecting peritoneal fluid, which is the fluid that surrounds the organs in the abdomen.

• Primary peritonitis is spontaneous bacterial peritonitis, meaning that the source of the infection is unknown. Enterobactericea, staphylococci, S. pneumoniae, viridans strep, and S. pyogenes are common causes

• Secondary peritonitis has a known source (e.g., a ruptured appendix or perforated bowel). Enterobacteriaceae, enterococci, Bacteroides, and other anaerobes frequently cause secondary peritonitis

• Peritoneal Dialysis fluid (dialysate) is used in chronic ambulatory peritoneal dialysis (CAPD) for end-stage renal failure patients. This fluid removes metabolic waste from the body. Common causative organisms include Staph, strep, GNR, and Corynebacterium spp.

• Pericardiocentesis is used to collect pericardial fluid from the pericardial space, which is the protective tissue surrounding the heart. Pericarditis is usually viral.

• Infectious/septic arthritis is often caused by S. aureus. Other organisms, including streptococci, N. gonorrhoea, H. influenzae, and Bacteroides spp., can also cause this type of arthritis.

• Amniocentesis is used to collect amniotic fluid

Urinary Tract

• The urinary tract comprises the kidneys, ureters, bladder, urethra, and prostate.

• Normal flora found in the urethra includes coagulase-negative staph, Corynebacterium, Micrococcus, streptococci, Enterobacteriaceae, anaerobic bacteria, yeast and mycoplasma

• Urinary tract infection (UTI) is a common infection of the urinary system, which is caused by microbial invasion of the urinary system. This can involve the bladder (cystitis), kidneys (pyelonephritis), or the urethral region (acute urethral syndrome) or urethritis

• Types of UTIs include cystitis (inflammation of the bladder), pyelonephritis (kidney infection), acute urethral syndrome (AUS - young women, dysuria, pyuria, bacteriuria), and urethritis

• UTIs originate from endogenous flora, primarily E. coli. Other causative bacteria include Klebsiella, Staphylococcus saprophyticus, S. aureus, enterococci, and Pseudomonas

• Routes of infection include ascending from the urethra to the bladder and kidneys, and descending via the bloodstream to the kidneys.

• Predisposing factors for UTIs include urinary tract abnormalities (e.g., enlarged prostate, kidney stones), instrumentation, such as catheterization, and underlying conditions, such as diabetes. Women are more prone to UTIs because of their shorter urethra, hormonal changes, sexual activity, and pregnancy

• Nosocomial UTIs are acquired in hospitals, often due to catheterization and instrumentation procedures

• Specimen collection should use sterile containers; Periurethral area needs cleaning and rinsing. Bedpans and urinals should not be used, and urine should be collected midstream after the first urine is passed to avoid contamination

• Specimens should remain in the bladder for as long as possible for the greatest specimen quality for analysis. First morning specimen is preferred.

• Acceptable specimens may be clean-catch midstream specimens, straight catheter, indwelling catheter, suprapubic aspirates, or cystoscopy specimens

• Urine specimens are transported at room temperature. If transport time exceeds 2 hours, the specimen should be refrigerated. Borne acid is an acceptable preservative

• Unacceptable specimens include pooled 24-hour urine, specimens from urine catheter tips (Foley catheters), and unrefrigerated urine (older than 2 hours). In addition, not all urine specimens are appropriate for anaerobic cultures, and suprapubic aspirates are preferred

• Urinalysis includes microscopic examination of an aliquot of the centrifuged urine specimen, followed by a wet mount of the sediment for WBCs and bacteria to assess for UTI

• Chemical analysis methods, such as leukocyte esterase and nitrate tests, may also be used for screening UTIs

Genital Tract and STDs

• Genital tract infections (GTIs) cover organs including vagina, cervix, uterus, fallopian tubes, and ovaries. STDs involve inflammation of the urethra (urethritis), vagina (vaginitis), and cervix (cervicitis).

• Types of STDs include infections by N. gonorrhoeae, C. trachomatis, U. urealyticum, Haemophilus, Candida albicans, and Trichomonas vaginalis infections, bacterial vaginosis, and certain viral infections (like herpes) and other organisms

• Bacterial vaginosis is often caused by a reduction in the number of lactobacilli

• Specimens collected include urogenital swabs (made of cotton, or rayon treated with charcoal), swabs inserted into the urethra or discharge, and swabs of the cervix or vagina obtained via speculum.

• Microscopy of vaginal specimens looks for clue cells (vaginosis) and intracellular gram-negative diplococci to detect N. gonorrhoeae. Cultures identify or rule out various microorganisms

• Many organisms in genital specimens require special culture conditions, including anaerobic cultures

• Incubation conditions depend on the organism and media and may vary. Typical aerobic conditions may be with 35°C in ambient air or GC cultures, using 5% CO2 versus high humidity and 35°C for anaerobic conditions

• Testing may vary depending on specimen type and quality. C. trachomatis, N. gonorrhoeae, B streptococci,* Listeria monocytogenes- may depend on PCR detection

• Specialized workup may be used assessing specimens depending on the type of the fluid, sample, and pathogen

This quiz covers essential concepts related to the central nervous system, including the structure and functions of the brain and spinal cord, cerebrospinal fluid, and various types of meningitis. Explore how infections can affect the CNS and the significance of maintaining its protective barriers. Test your knowledge on the impacts of trauma and surgical procedures on the CNS.