Norwalk virus outbreak carnival

To circumvent these obstacles to laboratory diagnosis, clinical and epidemiologic criteria were developed that correlate with the presence of NLVs in outbreaks of acute gastroenteritis During the early s, breakthroughs in cloning and sequencing of Norwalk virus and Southampton virus led to the development of sensitive molecular assays e.

These data demonstrate that NLVs are a common cause of outbreaks of nonbacterial gastroenteritis in the United States and similar findings have been reported in other countries In addition to improving detection rates of NLVs in outbreaks of gastroenteritis, advances in laboratory methods have also refined the epidemiologic investigation of these outbreaks.

This progress is well-illustrated in reports of recent outbreaks linked to contaminated water, oysters, and other food items In certain outbreaks, the detection of a genetically identical strain of NLV among patients from different geographic locations provided substantial evidence to support the link among the cases that was indicated by epidemiologic observations.

In other outbreaks, the detection in the implicated vehicle of NLVs with a sequence identical to that of the strain detected from the patients confirmed the causal link. Although diagnostic advances have improved the investigation of gastroenteritis outbreaks, they have also required that investigators collect clinical and environmental specimens accurately and in a timely manner and collaborate with the laboratory during the investigation. This report reviews recent advances in NLV diagnosis, and provides CDC's guidelines and recommendations for investigating gastroenteritis outbreaks, including methods for collecting specimens and preventing and controlling outbreaks.

Norwalk virus is the prototype strain of genetically and antigenically diverse single-stranded RNA ribonucleic acid viruses, previously called small round-structured viruses SRSVs , that are classified in the genus Norwalk-like viruses in the family Caliciviridae Other genera in the Caliciviridae family include "Sapporo-like viruses," which also cause gastroenteritis among both children and adults, and Lagovirus and Vesivirus , neither of which are pathogenic for humans.

The burden of NLV-caused endemic disease is unknown because simple and sensitive diagnostic assays are not readily available. However, the potential burden of NLV disease can be understood by examining the disease burden of gastroenteritis of all causes with the insights obtained during the limited number of studies in which newer diagnostics for NLVs have been applied. Annually, approximately ,, episodes of diarrhea leading to , hospitalizations and 3, deaths occur among adults in the United States In other countries e.

Although rotavirus is the leading cause of severe diarrhea among children 56 , data from recent studies demonstrate that NLVs also might be a factor in childhood gastroenteritis NLV-caused gastroenteritis has an average incubation period of hours and lasts hours. Illness is characterized by acute onset of nausea, vomiting, abdominal cramps, and diarrhea. Vomiting is relatively more prevalent among children, whereas a greater proportion of adults experience diarrhea.

Patients can experience vomiting alone, a condition first identified as winter vomiting disease Constitutional symptoms e. Although rare, severe dehydration caused by NLV gastroenteritis can be fatal, with this outcome occurring among susceptible persons e.

No long-term sequelae of NLV infection have been reported. Fecal-oral spread is probably the primary NLV transmission mode, although airborne and fomite transmission might facilitate spread during outbreaks Frequently during an outbreak, primary cases result from exposure to a fecally contaminated vehicle e. Previously, researchers believed that a person remained contagious hours after recovery from NLV gastroenteritis However, data from recent studies using more sensitive diagnostic assays demonstrate that this belief might require further evaluation.

Viral shedding in stool began 15 hours after virus administration and peaked hours after virus administration. Unexpectedly, viral antigen could be detected by ELISA in stool specimens collected 7 days after inoculation in both symptomatic and asymptomatic persons. Anecdotal evidence from outbreak investigations also demonstrates that viral shedding can occur for a prolonged period and in the absence of clinical illness 46,48, However, the epidemiologic significance of these findings is unclear.

Additional research is need to determine whether the viral antigen that is detectable for prolonged periods after recovery from illness is evidence of infectious virus or just a soluble antigen and to assess the time of maximal viral shedding so that control measures can focus on the period during which the person is most likely to be contagious. Characteristics of NLVs facilitate their spread during epidemics Table 1.

The low infectious dose of NLVs i. Prolonged duration of viral shedding that can occur among asymptomatic persons increases the risk for secondary spread and is of concern in foodhandler-related transmission. The ability of the virus to survive relatively high levels of chlorine 82 and varying temperatures i.

Because of the diversity of NLV strains, lack of complete cross-protection, and lack of long-term immunity, repeated infections can occur throughout life.

Studies of NLV immunity have been hampered by the inability of these viruses to be cultivated in cell lines, and thus, in vitro neutralization assays are not available. Certain studies also demonstrated, paradoxically, that persons with higher levels of preexisting NLV antibodies would probably experience illness if exposed to the virus 84, Researchers hypothesized that certain persons might be genetically more susceptible to NLV infection and disease. If true, this hypothesis could explain why those with greater levels of preexisting antibody are more likely to experience NLV infection and disease after reexposure to virus.

Outbreaks of NLV gastroenteritis occur in multiple settings. Protracted outbreaks of NLV disease have been reported among elderly persons living in institutional settings, e.

In certain cases, the outbreak was initially caused by a common-source exposure to a fecally contaminated vehicle e. Later, the outbreak spreads through person-to-person transmission among the residents; this spread is facilitated by the enclosed living quarters and reduced levels of personal hygiene that result from incontinence, immobility, or reduced mental alertness.

Because of underlying medical conditions, the disease among these persons can be severe or fatal. A report from Minnesota demonstrates the relevance of NLVs as a cause of foodborne outbreaks Investigations of foodborne NLV outbreaks have implicated multiple food items, including oysters, salads, sandwiches, cakes, frosting, raspberries, drinking water, and ice , In certain outbreaks, the implicated food is fecally contaminated with NLVs at its source e.

However, foodhandlers might contaminate food items during preparation. The risk for contamination through foodhandlers is increased when the food item is consumed without further cooking e. Passengers and crew members on cruise ships and naval vessels are frequently affected by outbreaks of NLV gastroenteritis 35,92, These ships dock in countries where levels of sanitation might be inadequate, thus increasing the risk for contamination of water and food taken aboard or for having a passenger board with an active infection.

After a passenger or crew member brings the virus on board, the close living quarters on ships amplify opportunities for person-to-person transmission. Furthermore, the arrival of new and susceptible passengers every 1 or 2 weeks on affected cruise ships provides an opportunity for sustained transmission during successive cruises.

NLV outbreaks extending beyond 12 successive cruises have been reported Consequently, efforts to prevent both the initial contamination of the implicated vehicle and subsequent person-to-person NLV transmission will prevent the occurrence and spread of NLV gastroenteritis outbreaks.

Theoretically, any food item can potentially be infected with NLVs through fecal contamination. However, certain foods are implicated more often than others in outbreaks of NLV gastroenteritis. Shellfish e. In addition, cooking e. Until reliable indicators for routine monitoring of viral contamination of harvest waters and shellfish are available, measures to prevent the contamination of harvest waters with human waste e.

Food contamination by infectious foodhandlers is another frequent cause of NLV gastroenteritis outbreaks. Because of the low infectious dose of NLVs and the high concentration of virus in stool, even a limited contamination can result in substantial outbreaks. Ready-to-eat foods that require handling but no subsequent cooking e. Previously, the exclusion of ill foodhandlers for hours after resolution of illness was recommended to prevent outbreaks caused by foodhandlers Data from recent human volunteer and epidemiologic studies demonstrate that viral antigen can be shed for a longer duration after recovery from illness and in the absence of clinical disease.

Although data are limited regarding whether this detectable viral antigen represents infectious virus, foodhandlers should be required to maintain strict personal hygiene at all times. Although waterborne outbreaks are far less common than foodborne outbreaks, NLV gastroenteritis outbreaks have been associated with sources of contaminated water, including municipal water, well water, stream water, commercial ice, lake water, and swimming pool water. Because current analytic methods do not permit direct monitoring of NLVs in water, indicator organisms e.

However, because the size, physiology, and susceptibility to physical treatment and disinfection of bacterial indicators differ from those of NLVs, inherent limitations of this approach exist.

Until reliable methods for assessing the occurrence and susceptibility to treatment of NLVs are available, prevention methods should focus on reducing human waste contamination of water supplies. If drinking or recreational water is suspected as being an outbreak source, high-level chlorination i. Person-to-person spread of NLVs occurs by direct fecal-oral and airborne transmission.

Such transmission plays a role in propagating NLV disease outbreaks, notably in institutional settings e. Although interruption of person-to-person transmission can be difficult, certain measures might help.

Frequent handwashing with soap and water is an effective means of prevention. Because spattering or aerosols of infectious material might be involved in disease transmission, wearing masks should be considered for persons who clean areas substantially contaminated by feces or vomitus e. Soiled linens and clothes should be handled as little as possible and with minimum agitation. They should be laundered with detergent at the maximum available cycle length and then machine dried.

Because environmental surfaces have been implicated in the transmission of enteric viruses, surfaces that have been soiled should be cleaned with an appropriate germicidal product e. In situations in which the epidemic is extended by periodic renewal of the susceptible population e. The following sections provide a summary of the commonly available diagnostic methods, which are extensively reviewed elsewhere Under the electron microscope, NLVs can be identified by their characteristic morphology.

In one type of IEM, convalescent-phase serum from patients is coated on the examination grid of the microscope before stool specimens are applied. The antibody on the grid traps homologous virus, thereby increasing diagnostic yield. However, IEM has certain disadvantages, the greatest of which is that success is highly dependant on the skill and expertise of the microscopist. Furthermore, the virus might be totally masked if a large excess of antibody is present, resulting in a false-negative test.

The expression in baculoviruses of the capsid proteins of NLVs that self-assemble into stable virus-like particles has allowed the detection of these viruses by ELISAs. To develop assays to detect virus in fecal specimens, the expressed capsid antigens have been used to generate hyperimmune antibodies in laboratory animals.

To date, these assays have been type-specific, but broadly reactive tests are under development. The baculovirus-expressed viral antigen can be directly used for detection of antibodies to NLVs in patient's sera by enzyme immunoassay. Because certain adults have preexisting immunoglobulin G IgG antibodies to NLVs, a single serum specimen is insufficient to indicate recent infection.

In outbreak settings, if at least half of affected persons seroconvert to a specific NLV, that viral strain can be designated as etiologic. Titers can begin to rise by the fifth day after onset of symptoms, peak at approximately the third week, and begin to fall by the sixth week.

Hence, for IgG assays, the acute-phase serum should be drawn within the first 5 days and the convalescent-phase serum during the third to sixth weeks. In certain cases where diagnosis is critical e.

In addition to potential difficulties in obtaining an adequate number of serum specimens during outbreaks, serologic assays are currently limited by the fact that the available array of expressed NLV antigens is insufficient to detect all antigenic types of NLVs.

High sensitivity of these assays i. Efforts are ongoing to develop universal or degenerate primers that would detect the majority of NLV strains that cause gastroenteritis outbreaks. Application of new molecular diagnostics has expanded the scope of outbreak investigations, as demonstrated in recent outbreaks Table 2 , because outbreak source vehicles e. However, these methods are not sufficiently developed to be routinely applied.

Through nucleotide sequencing, establishing an irrefutable genetic link between outbreaks that occur through a single contaminated vehicle that is distributed in multiple geographic locations is possible. Specimen collection for viral testing should begin on day 1 of the epidemiologic investigation. The outbreak on the Amsterdam provoked the second outbreak investigation this year for Holland America.

The cruise line, which is owned by Carnival, faces a possible class-action lawsuit in Canada after people on its ship, the Ryndam, fell ill on a Vancouver-based cruise. Holland America canceled a subsequent sailing to sanitize the Ryndam, and last month performed a day scrub-down on the Amsterdam — which included steam-cleaning , square feet of carpet and disinfecting the poker chips.

Absolutely not. The line also came to the attention of authorities when 38 people on its Statendam ship came down with Norwalk-like symptoms last month. The CDC did not investigate the incident because only 2 percent of the passengers were infected, the agency said. The Norwalk-like virus — actually a family of viruses similar to and named for a specific bug identified in a outbreak in Norwalk, Ohio — is a seasonal illness that peaks in the colder months.

It is relatively common in group settings, such as nursing homes, hospitals and schools, health officials said. Sailing the sickening seas Two more cruise ships report gastrointestinal infections The Fascination is the third ship to experience a gastrointestinal illness outbreak in recent weeks. Story Tools. House votes to keep U. A Time Warner Company. All Rights Reserved.

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