Clinical Manifestations

The clinical presentation depends in large part on the site of the body infected by ExPEC.

• UTI: The urinary tract is the site most frequently infected by ExPEC; see Chap. 147 Dysuria, Urinary Tract Infections, Bladder Pain, and Interstitial Cystitis for more details. E. coli causes 80-90% of ∼6-8 million episodes of acute uncomplicated UTI in ambulatory premenopausal women.
• Abdominal and pelvic infection: The abdomen and pelvis represent the second most common site of infection by ExPEC, which may be isolated in the setting of a polymicrobial infection; see Chap. 84 Intraabdominal Infections for more details. Syndromes include peritonitis, intraabdominal abscesses, and cholangitis.
• Pneumonia: ExPEC is generally the third or fourth most commonly isolated GNB in hospital-acquired pneumonia and can be a common cause of pneumonia in pts residing in long-term-care facilities; see Chap. 134 Pneumonia, Bronchiectasis, and Lung Abscess for more details.
• Meningitis: E. coli is one of the two leading causes of neonatal meningitis (the other being group B Streptococcus). Strains with the K1 capsular serotype are generally involved.
• Cellulitis/musculoskeletal infection: E. coli often contributes to infection of decubitus ulcers and diabetic lower-extremity ulcers, cellulitis, and burn-site or surgical-site infections. Hematogenously acquired osteomyelitis, particularly vertebral, is more commonly caused by E. coli than is generally appreciated. See Chap. 87 Infections of the Skin, Soft Tissues, Joints, and Bones for more details.
• Bacteremia: E. coli bacteremia can arise from primary infection at any site, but originates most commonly from the urinary tract (50-67% of episodes) and next most commonly from the abdomen (25% of episodes). E. coli bacteremia is almost always clinically significant and may be associated with sepsis. Endovascular infections are rare but have been described.

Diagnosis

ExPEC grows readily on standard media under either aerobic or anaerobic conditions. More than 90% of strains ferment lactose and are indole positive.

Microbiology and Clinical Manifestations

At least five distinct pathotypes of intestinal pathogenic E. coli exist; see Chap. 85 Infectious Diarrheas and Bacterial Food Poisoning for more details. As mentioned above, these strains are rarely encountered as part of the commensal microbiota in healthy individuals.

• Shiga toxin-producing E. coli (STEC)/enterohemorrhagic E. coli (EHEC)/Shiga toxin-producing enteroaggregative E. coli (ST-EAEC): In addition to diarrhea, STEC/EHEC infection results in the hemolytic-uremic syndrome (HUS) in 2-8% of pts, particularly those who are very young or elderly. ST-EAEC results in a higher rate of HUS (∼20%), with a higher incidence among adults, especially young women.
  • STEC/EHEC/ST-EAEC is associated with ingestion of contaminated food (e.g., undercooked ground beef, fresh produce) and water; person-to-person transmission (e.g., at day-care centers) is an important route for secondary spread.
  • Disease can be caused by <10² colony-forming units (CFU) of STEC/EHEC/ST-EAEC.
  • In contrast to the other pathotypes, STEC/EHEC/ST-EAEC (including E. coli O157:H7) causes infection more frequently in industrialized countries than in developing countries.
• Enterotoxigenic E. coli (ETEC): These strains are a major cause of endemic diarrhea among children residing in tropical and low-income countries and are the most common agent of traveler's diarrhea; 10⁶ -10⁸ CFU are needed to cause disease.
• Enteropathogenic E. coli (EPEC): EPEC is an important cause of diarrhea among infants in developing countries.
• Enteroinvasive E. coli (EIEC): EIEC, an uncommon cause of diarrhea, produces inflammatory colitis (stools containing mucus, blood, and inflammatory cells) similar to that caused by Shigella and primarily affects children and travelers in developing countries; 10⁸ -10¹⁰ CFU are needed to cause disease.
• Enteroaggregative and diffusely adherent E. coli (EAEC): EAEC was initially described in young children in developing countries. More recent studies indicate that EAEC infection requires a large inoculum and may be a common cause of prolonged, watery diarrhea in all age groups in industrialized countries.

Diagnosis

Specific diagnosis is usually unnecessary for management, but detection of STEC/EHEC/ST-EAEC has public health importance. To detect the latter, simultaneous culture (screening for E. coli strains that do not ferment sorbitol followed by serotyping for O157) and testing for Shiga toxins or toxin genes is recommended.

Epidemiology

K. pneumoniae colonizes the colon in 5-35% of healthy individuals and, from a medical standpoint, is the most important Klebsiella species. K. oxytoca primarily causes infections in long-term care and hospital settings. K. pneumoniae subspecies rhinoscleromatis, which causes rhinoscleroma, and K. pneumoniae subspecies ozaenae, which causes chronic atrophic rhinitis, infect pts in tropical climates.

Clinical Manifestations

As in other GNB infections, the clinical presentation depends on the infected anatomic site.

• Pneumonia: Klebsiella is a common cause of pneumonia among residents of long-term care facilities and hospitalized pts. In Asia and South Africa, community-acquired pneumonia due to hypervirulent strains of K. pneumoniae is increasingly common, particularly among younger, healthy pts.
  • The presentation is similar to that of pneumonia caused by other enteric GNB, with purulent sputum production and pulmonary infiltrates on CXR.
  • Infection can progress to pulmonary necrosis, pleural effusion, and empyema.
• UTI: K. pneumoniae causes 1-2% of cases of uncomplicated cystitis and 5-17% of cases of complicated UTI.
• Abdominal infections: Klebsiella causes a spectrum of disease similar to that of E. coli, but with less frequent occurrence. Hypervirulent strains have become a common cause of monomicrobial community-acquired liver abscess, spontaneous bacterial peritonitis, and splenic abscess.
• Bacteremia: Bacteremia can arise from a primary infection at any site; infections of the urinary tract, respiratory tract, and abdomen (especially hepatic abscess) each account for 15-30% of episodes.
• Other infections: Klebsiella cellulitis or soft-tissue infection most frequently affects devitalized tissue and immunocompromised hosts. Klebsiella can also cause endophthalmitis, nosocomial sinusitis, and osteomyelitis.

Diagnosis

Klebsiellae usually ferment lactose, although the K. pneumoniae subspecies rhinoscleromatis and ozaenae are nonfermenters and are indole negative.

Epidemiology

P. mirabilis is part of the normal microbiota in 50% of healthy people and causes 90% of Proteus infections. P. vulgaris and P. penneri are isolated primarily from pts in hospitals and long-term care facilities.

Clinical Manifestations

Most Proteus infections arise from the urinary tract. Proteus species account for 1-2% of uncomplicated UTIs, 5% of hospital-acquired UTIs, and 10-15% of complicated UTIs (especially those associated with urinary catheters).

• Proteus produces high levels of urease that result in alkalinization of urine and ultimately in formation of struvite and carbonate-apatite calculi.
• Infections at other sites are uncommon but include pneumonia, abdominal infections, soft-tissue infections, and bacteremia.

Diagnosis

Proteus strains are typically lactose negative, produce H₂S, and exhibit swarming motility on agar plates. P. mirabilis and P. penneri are indole negative, whereas P. vulgaris is indole positive.