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 Central Nervous System Infections

Acute Bacterial meningitis

 Neonates (0-2 weeks old)

• Streptococcus agalactiae (Group b streptococcus)
• Escherichia coli
• Listeria monocytogenes

Neonates (0-3 months)

• Streptococcus agalactiae
• Escherichia coli
• Listeria monocytogenes
• Streptococcus pneumoniae
• Haemophilus influenzae

3 months to 50 years of age

• Streptococcus pneumoniae
• Neisseria meningitidis
• Haemophilus influenzae

Over 50 years of age

• Streptococcus pneumoniae
• Listeria monocytogenes
• As the population ages, Haemophilus influenzae will become more prevalent in this age group

Nosocomial (hospital acquired) and immunocompromised patients

• Escherichia coli
• Klebsiella spp.
• Staphylococcus aureus
• Streptococcus pneumoniae

Viral (aseptic) meningitis and encephalitis (90% of cases in patients under 30 years old)

• Enteroviruses (70%; late summer and early fall)
• Arboviral meningoencephalitis (summer via tick or mosquito; West Nile virus, Eastern Equine Encephalitis virus, Western Equine Encephalitis virus, St. Louis Encephalitis virus, California group Encephalitis viruses, Powassan Encephalitis virus)- are the most common cause of episodic encephalitis in the US.
• Mumps (late winter and early spring)
• Herpes simplex virus (sporadic)
• HIV (sporadic)
• Rabies virus (rare)

Granulomatous Meningitis (Chronic meningitis)

• Mycobacterium tuberculosis
• Cryptococcus neoformans

Spinal cord

• Clostridium tetanus*
• Polio virus

Skin (Integument) Infections

There are a huge number of infectious diseases of this the largest organ of the human anatomy. Therefore, only the more common bacterial, viral and fungal microbes are mentioned here.

Common Bacterial Infections.

• Staphylococcus aureus - impetigo, bullous impetigo, scalded skin syndrome, folliculitis, furuncles, carbuncles, cellulitis, myositis and toxic shock syndrome.
• Streptococcus pyogenes - impetigo, scarlet fever, erysipelas, necrotizing fasciitis, and streptococcal toxic shock syndrome. 
• Propionibacterium acne - acne

Common Viral Infections.

• Herpes Simplex 1 and 2 viruses- oral and genital herpes
• Papilloma viruses – warts, genital warts, cervical dysplasia and cervical carcinoma
• Common childhood rashes (exanthems) are caused by
  • Coxsackie viruses and Echoviruses (enteroviral rashes),
  • Erythrovirus B19 (formerly Parvovirus B19; Erythema Infectiosum)
  • Human Herpes virus 6B (Exanthem subitum or Roseola)
  • Human Herpes Virus-7 (Exanthem subitum or Roseola)
  • Varicella-Zoster virus (Chickenpox)
  • Measles virus (Rubeola)
  • Rubella virus (Rubella).

Common Fungal Infections.

• Malassezia furfur- Tinea versicolor
• The dermatophytes (Microsporum, Trichophyton and Epidermophyton) - Tinea pedis, Tinea corporis, Tinea capitis, Tinea manus and Tinea cruris.
• Candida albicans - intertrigo, perlèche, folliculitis, paronchyia and onychomycosis.

Ear Infections

Otitis Media

• Streptococcus pneumoniae
• Moraxella catarrhalis
• Haemophilus influenzae (nontypable)

Otitis externa

• Pseudomonas aeruginosa*
• Staphylococcus aureus

Eye and Eyelid Infections

Anterior Blepharitis

• Staphylococcus aureus or Staphylococcus epidermidis

Hordeola (stye)

• Staphylococcus aureus

Periorbital (Preseptal) Cellulitis

• Streptococcus pneumoniae in young children
• Staphylococcus aureus or Streptococcus pyogenes post-traumatic

Orbital (Postseptal) Cellulitis

• Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae, Haemophilus influenzae and Enterobacteriaceae

Dacryocystitis

• Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae, Streptococcus pyogenes, and Pseudomonas aeruginosa

Conjunctivitis

• Viral- Adenoviruses*, Herpes Simplex viruses’ types 1 and 2 (less common but more serious infection)
• Bacterial (pinkeye)- Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Pseudomonas aeruginosa, Neisseria gonorrhoeae and Neisseria meningitidis
• Chlamydial- Chlamydia trachomatis

Keratitis

• Bacteria*
  • Gram positive bacteria (Streptococcus pneumoniae, Staphylococcus epidermidis, Streptococcus pyogenes, Streptococcus viridans, enterococci and Peptostreptococcus) are most frequently obtained with the most common of them being Staphylococcus aureus.
  • Gram positive bacilli that cause keratitis include Corynebacterium diphtheriae, Bacillus and Clostridium
  • Gram negative bacilli that cause keratitis include Pseudomonas aeruginosa, Proteus mirabilis, Klebsiella pneumoniae, Serratia marcescens, Escherichia coli and Aeromonas hydrophila. Pseudomonas aeruginosa is one of the most destructive of the bacterial causes of keratitis.
  • Gram negative cocci or coccobacilli that cause keratitis include Neisseria gonorrhoeae, Neisseria meningitidis, Moraxella, Pasteurella multocida and Acinetobacter.
  • Ocular lymphogranuloma venereum is more serious than simple chlamydial conjunctivitis because corneal scars, conjunctival scars, and micropannus formation can occur (serotypes L1-L3 of Chlamydia trachomatis).
• Viruses
  • Herpes Simplex 1 and 2*- most common of viruses
  • Adenoviruses- epidemic keratoconjunctivitis
  • Varicella Zoster virus

Respiratory Tract Infections

Acute Rhinosinusitis

• Usually caused by various respiratory viruses.

Acute Bacterial Rhinosinusitis

• Streptococcus pneumoniae
• Haemophilus influenzae (nontypable)

Common cold (Rhinitis)

• Rhinoviruses*
• Coronaviruses

Pharyngitis

• Adenovirus
• Herpes Simplex virus
• Epstein Barr Virus
• Coxsackie viruses
• Remember Streptococcus pyogenes (group A streptococcus is important because of the complications that can result (rheumatic fever).

Viral Croup

• Parainfluenza virus
• Influenza virus
• Respiratory syncytial virus (most common cause of bronchiolitis in children under 1 year of age).

Bacterial tracheitis

• Staphylococcus aureus

Epiglottitis

• Haemophilus influenzae type b (very rare now due to the Hib vaccine)

Bronchitis

• Respiratory viruses that infect the upper respiratory tract: influenza viruses A and B, parainfluenza viruses, adenovirus, respiratory syncytial virus, herpes simplex virus, rhinovirus, coxsackievirus A and B, and echovirus.
• Mycoplasma pneumoniae
• Chlamydophila pneumoniae (TWAR agent)- 5% of cases
• Streptococcus pyogenes

Bronchiolitis

• Respiratory Syncytial virus (RSV)

Pneumonia

Neonatal (0-1 month)

• Escherichia coli
• Streptococcus agalactiae (group B streptococcus)

Infants (1-6 month)

• Chlamydia trachomatis (afebrile pneumonia with staccato cough)
• RSV

Children (6month-5 year)

• RSV
• Parainfluenza virus

Children (5-15 year)

• Mycoplasma pneumoniae
• Influenza virus type A

Young Adults (16-30 yr)

• Mycoplasma pneumoniae

Older Adults

• Streptococcus pneumoniae*
• Haemophilus influenzae

Gastrointestinal tract infections

Infections of the Teeth

• Dental caries- Streptococcus mutans, Streptococcus sobrinus, low-pH tolerant Streptococcus spp., Lactobacillus casei, Actinomyces spp., and Bifidobacterium spp.
• Gingivitis- The more dental plaque that accumulates on the teeth the more likely a patient will develop gingivitis. The plaque leading to gingivitis contains higher numbers of Gram negative anaerobic bacilli and spirochetes.
• Necrotizing ulcerative gingivitis (NUG: trench mouth)- the dental biofilm/plague usually contains a lot of Fusobacterium spp., Prevotella intermedia, and especially spirochetes (Treponema denticola).
• Chronic periodontitis- is a polymicrobial process; biofilms (plaque) containing higher numbers of Gram negative anaerobic bacilli and spirochetes. Certain organisms, when present in plaque will increase the risk of chronic periodontitis developing.
  • Red complex organisms (high risk): Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola.
  • Orange complex organisms (moderate risk): Fusobacterium nucleatum, Prevotella intermedia, Prevotella nigrescens, Parviomonas micra, Eubacterium nodatum, and various Camplylobacter species (e.g., C. rectus).
  • Yellow complex organisms (low risk): Streptococcus intermedius, Streptococcus sanquinis, Streptococcus oralis, Streptococcus mitis, and Streptococcus gordonii.
• Aggressive periodontitis- The plaque microflora in aggressive periodontitis is similar to chronic periodontitis. However, the presence of certain bacteria in the plaque increases the risk for this disease to develop (Aggregatibacter actinomycetemcomitans or Eikenella corrodens in concert with Fusobacterium nucleatum). Sparse amounts of biofilm/plaque are generally found relative to degree of periodontal destruction.

Ludwig’s Angina

• Streptococcus, Bacteroides, Fusobacterium and/or Staphylococcus aureus

Infections of the Mouth and Tongue

• Herpes Simplex viruses 1 and 2 (gingivostomatitis or cold sores)
• Candida albicans (oral candidiasis)

Angular Cheilitis

• Candida albicans

Parotitis

• Mumps virus- benign viral parotitis
• Staphylococcus aureus- acute bacterial parotitis

Esophagitis- usually only seen in immunocompromised patients

• Candida albicans*
• Cytomegalovirus (CMV) Herpes Simplex Virus (HSV), Human Immunodeficiency virus (HIV), Varicella Zoster Virus (VZV)

Peptic Ulcer Disease

• Helicobacter pylori

Intestinal Infections- Bacterial (can be inflammatory [blood and mucus small volume; fecal wbc's present] or noninflammatory [large volume watery stools; fecal wbc's NOT present]

Inflammatory ones

• Campylobacter jejuni
• Escherichia coli (EIEC)
• Escherichia coli (EHEC)
• Salmonella typhimurium
• Salmonella typhi (get also fever and headache; sometimes no diarrhea)
• Shigella dysenteriae type 1 (lots of PMN's)
• Shigella sonnei/flexneri
• Yersinia enterocolitica
• Clostridium difficile (can be both inflammatory and non-inflammatory)

Non-inflammatory ones

• Escherichia coli (EPEC)
• Escherichia coli (ETEC)
• Escherichia coli (EAEC)
• Vibrio cholerae
• Clostridium difficile (can be both inflammatory and non-inflammatory)

Parasitic infections of the intestine

• Giardia lamblia*
• Entamoeba histolytica
• Cryptosporidium parvum
• Cyclospora cayetanensis
• Enterobius vermicularis
• Taenia saginata
• Taenia solium
• Hymenolepis nana
• Ascaris lumbricoides
• Necator americanus
• Strongyloides stercoralis

Viral Gastroenteritis

• Noroviruses* (winter vomiting disease- most common in industrialized countries for all age groups)
• Rotavirus (winter infant diarrhea- next most common in infants and children; after Norovirus)
• Adenoviruses
• Astroviruses

Food poisoning- intoxications

• Staphylococcus aureus*
• Bacillus cereus
• Clostridium perfringens
• Clostridium botulinum

Viral Hepatitis- Infections of the Liver

• Hepatitis A virus
• Hepatitis C virus
• Hepatitis B virus
• Hepatitis D virus
• Hepatitis E virus

Infections of the Bones and Joints

Osteomyelitis

• Staphylococcus aureus*
• Streptococcus sp.
• Members of the Enterobacteriaceae

Septic arthritis

• Neisseria gonorrhoeae (most common in sexually active young adults)
• Staphylococcus aureus*

Infections of the Heart

Pericarditis

• Viral pericarditis*- Enteroviruses [Coxsackieviruses (A and B) and Echovirus (type 8)]
• Purulent pericarditis- rare- Staphylococcus aureus, Streptococcus pneumoniae and other streptococci
• Chronic pericarditis- rare- Mycobacterium tuberculosis and various fungi (Candida sp.)

Myocarditis

• Enteroviruses (Coxsackievirus B is the most common)*

Endocarditis

·        Native valve- Streptococcus sp. (60-80%, viridans streptococci (30-40%), Streptococcus bovis (10%), Enterococci (S. faecalis and S. faecium; 5-18%) and Staphylococci (20-35%, usually Staphylococcus aureus)

·        Intravenous drug users- Staphylococcus aureus (50%) and gram-negative bacilli (15%; Pseudomonas aeruginosa is most the common gram-negative).

·        Prosthetic valve infections

• Early (within 2 months of surgery) - Staphylococcus (50%; coagulase positive and coagulase negative), gram-negative aerobic bacilli (20%) and fungi (5%).
• Late (more than 2 months post surgery) - viridans Streptococcus sp. (35%), coagulase negative staphylococci (20%), and Staphylococcus aureus (10%).

Rheumatic Heart Disease

• Streptococcus pyogenes

Hematopoietic/Lymphoreticular Infections

Infections of the Lymphocytes

• Acquired Immunodeficiency Syndrome (HIV/AIDS)- T-lymphocytes 
• Infectious Mononucleosis- B-lymphocytes
• Cytomegalovirus Infections- T-lymphocytes and macrophages

Infections of the Phagocytic Cells

• Cat-scratch disease – Bartonella henselae  
• Tularemia – Francisella tularensis 
• Ehrlichiosis/Anaplasmosis - Ehrlichia chaffeensis, Ehrlichia ewingii and Anaplasma phagocytophilum
• Q fever- Coxiella burnetii       
• Brucellosis- Brucella sp. Plague- Yersinia pestis

Infection of the Erythrocytes

• Babesia- Babesia microti
• Malaria- Plasmodium sp.

Infection of the Endothelial Cells

• Bacillary Angiomatosis/Hepatica peliosis- Bartonella henselae or Bartonella quintana  
• Endemic relapsing fever- Borrelia sp. (15 different species; B. hermsii, B. parkeri)
• Epidemic Hemorrhagic fever- Sin Nombre virus (Hantavirus- hantavirus pulmonary syndrome)
• Rocky Mountain Spotted Fever- Rickettsia rickettsii

Bacterial Sepsis

Neonates

• E.coli*
• Streptococcus agalactiae (group b strep.)

Adults (Systemic Inflammatory Response Syndrome, Sepsis, Septic Shock)

• Most are due to bacterial infections. 50% due to Gram negative bacteria; 50% due to Gram positive bacteria. It depends on the location of the site of the initial infection. Most common sites of infection leading to sepsis are lungs, abdomen, and urinary tract (ex. urinary tract think Escherichia coli; community acquired pneumonia think Streptococcus pneumoniae).

Infections of the Genitourinary Tract

Cystitis and Pyelonephritis

• Escherichia coli*

Acute bacterial Prostatitis

• Escherichia coli*

Vaginitis

• Bacterial Vaginosis* (BV) due to Gardnerella vaginalis, Atopobium vaginae, Mycoplasma hominis and various anaerobic bacteria including Mobiluncus sp., and Prevotella sp.
• Candida albicans
• Trichomonas vaginalis

Sexually Transmitted Infections (STI’s) of the Genitourinary Tract

Genital Ulcerative Diseases

• Genital Herpes- HSV-2* (80%),
• HSV-1 (20%) Syphilis- Treponema pallidum
• Chancroid- Haemophilus ducreyi
• Granuloma Inguinale- Klebsiella granulomatis (formerly Calymmatobacterium granulomatis)    
• Lymphogranuloma Venereum- Chlamydia trachomatis

Urethritis

• Chlamydia trachomatis*
•  Neisseria gonorrhoeae

Cervicitis

• Chlamydia trachomatis*
• Neisseria gonorrhoeae

Other STI’s

Acute Pelvic Inflammatory Disease

• Chlamydia trachomatis*
• Neisseria gonorrhoeae

Genital Warts

• Human Papilloma virus (HPV types 6 and 11 most common for wart-like lesions; HPV types 16 and 18 most common for with cervical dysplasia and carcinoma.)

Epididymitis

• Sexually active men aged <35 years-  Chlamydia trachomatis or Neisseria gonorrhoeae
• Men >35 years of age- gram-negative enteric bacteria

Ectoparasitic Infections

Scabies

• Sarcoptes scabiei var hominis

Pediculosis

• Pediculus humanus capitis (head louse)
• Pediculus humanus corporis (body louse)
• Pthirus pubis (pubic louse)

* = Most common; please note this is not an exhaustive list and does not include all possible etiologies for a particular disease.

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