Other Vibrio Species - Clinical Tree

In addition to organisms that cause cholera (see Chapter 158 ), several other Vibrio species cause vibriosis. These can be divided into invasive species primarily associated with bloodstream and wound infections (e.g., V. vulnificus ) and species that typically cause gastroenteritis (e.g., V. parahaemolyticus ). With the exception of V. parahaemolyticus and V. vulnificus biogroup 3, these organisms rarely cause outbreaks.

Description of the Pathogens

Vibrios are bacteria of the family Vibrionaceae . They are fermentative, facultatively anaerobic, gram-negative bacilli with a single polar flagellum. Except for V. cholerae and its close relatives , all Vibrio species are halophilic (salt-requiring). Despite reclassification of V. hollisae and V. damsela as Grimontia hollisae and Photobacterium damselae , respectively, these two species are still included in the vibrios.

Possible virulence factors have been described for the nontoxigenic Vibrio species, including cell-associated adhesins, extracellular toxins, and proteases; the actual role of these factors in disease is unknown. Some V. cholerae non-O1, non-O139 strains, and V. mimicus strains produce cholera toxin. Little is known about immunity against nontoxigenic vibrios.

Vibrios are free-living inhabitants of marine coastal waters and, occasionally, brackish inland lakes and streams; their presence does not indicate fecal contamination. Water surface temperatures and salinity affect concentrations of most Vibrio species. Most Vibrio infections occur during summer and fall when surface waters are relatively warm. V. vulnificus uses iron for growth; people with elevated iron levels are at higher risk for infection.

Epidemiology

An estimated 80,000 cases of vibriosis, including 500 hospitalizations and 100 deaths, occur in the US yearly, with most infections in men. ^, The incidence of vibriosis has been increasing in the US. V. parahaemolyticus is the nontoxigenic Vibrio species most frequently identified from clinical specimens in the US; it accounts for approximately one-half of culture-confirmed human infections. V. alginolyticus and V. vulnificus are the next most commonly identified species ( Table 159.1 ). Vibriosis is reported more commonly from coastal than inland states. Estuarine filter feeders (e.g., oysters, clams, mussels, shrimp, and crabs) can sequester and concentrate vibrios. Vibriosis occurs most commonly in people who have consumed raw or undercooked seafood, especially shellfish. It also can occur after exposure of a wound to seawater. ^, Not all infections are detected because many laboratories do not routinely use media selective for vibrios; however, increased use of culture-independent diagnostic tests (CIDTs) allows for the identification of infections that may have been missed previously. For decades, infections with toxigenic V. cholerae serogroups O1 and O139 were nationally notifiable; in 2007, infection caused by any Vibrio species became nationally notifiable; and in 2017, CIDT-detected cases became nationally notifiable.

TABLE 159.1

Species of the Family Vibrionaceae Most Commonly Associated With Culture-confirmed Vibriosis in the US, 2014–2018

Species of the Family Vibrionaceae	Site of Isolation
Species of the Family Vibrionaceae	Blood	Stool	Wound	Percentage of Reported Vibrio Isolates ^a (%)
*Vibrio parahaemolyticus*	+	+++	++	44
*Vibrio alginolyticus*	+	+	+++	18
*Vibrio vulnificus*	+++	+	++	12
*Vibrio cholerae* , nontoxigenic	++	+++	+	8
*Vibrio fluvialis*	+	+++	++	6
*Vibrio mimicus*	+	+++	+	2
*Grimontia hollisae*	+/−	+++	+	1

+++, common (51%–100% of isolates); ++, occasional (10%–50% of isolates); +, infrequent (1%–9% of isolates); +/−, rare (<1% of isolates).

a Based on 7106 culture-confirmed infections reported to the Centers for Disease Control and Prevention’s Cholera and Other Vibrio Illness Surveillance System, 2014–2018. Species constituting ≥1% of reported isolates are listed.

Vibrio vulnificus

In 1979, before V. vulnificus was named, scientists at the Centers for Disease Control and Prevention (CDC) described the organism and the illness it causes. It is the Vibrio species most commonly associated with life-threatening illness in the US. The CDC receives reports of, on average, 165 illnesses, 137 hospitalizations, and 28 deaths from V. vulnificus yearly (CDC, unpublished data, 2014–2018). It is the most lethal infection associated with raw oyster consumption; however, most V. vulnificus illnesses are wound infections associated with exposure to seawater. ^, V. vulnificus illnesses have been reported from all US coastal regions. The number of patients whose exposure was to seawater along the Atlantic Coast has increased in recent years. The organism causes 2 major syndromes: primary bacteremia and wound infection.

Infections are classified as primary bacteremia when V. vulnificus is isolated from a normally sterile site of a patient without a preceding wound infection. Among US patients with V. vulnificus primary bacteremia between 1988 and 1996, 96% consumed raw oysters in the 7 days before symptoms began. Almost all patients with primary bacteremia have an underlying condition, such as liver disease, malignancy, hemochromatosis, or immunocompromise. ^, The CDC has issued guidance regarding the risks of consuming raw or undercooked seafood, particularly for people with underlying conditions ( Box 159.1 ).

BOX 159.1

Centers for Disease Control and Prevention Guidance Regarding Vibrio Infection

Information from Centers for Disease Control and Prevention. Vibrio Species Causing Vibriosis ; 2020. https://www.cdc.gov/vibrio/index.html .

People should be informed that the consumption of raw or undercooked seafood and open wound contact with warm seawater increases the risk of Vibrio infection.
People who are immunocompromised, especially those with chronic liver disease, are at the highest risk for severe Vibrio infection.
To ensure the appropriate diagnosis of infection, clinicians should request microbiologic culture with selective media when Vibrio is suspected.
Clinical laboratories should send all Vibrio isolates to their state public health laboratory for confirmation and species identification. (If a positive result of a culture-independent test was used to diagnose Vibrio infections, a specimen should be obtained for culture. )

Wound infection with V. vulnificus typically occurs through the exposure of a wound to warm seawater. Most infected persons have an underlying condition; infections rarely occur in healthy children. ^, Severe wound infections with V. vulnificus biogroup 3 have been reported from Israel among previously healthy persons who handled live tilapia.

Vibrio parahaemolyticus

V. parahaemolyticus causes sporadic infections and outbreaks of gastroenteritis. ^, Most patients report eating raw oysters in the week before illness began. The most recent outbreaks were linked to imported crab meat (in 2018) and imported oysters (in 2019). ^, Soft tissue infections are rare. ^,

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