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Published Date: 2011-11-18 11:33:37
Subject: PRO/AH/EDR> Paralytic shellfish poisoning - USA: (AK)
Archive Number: 20111118.3395

PARALYTIC SHELLFISH POISONING - USA: (ALASKA)
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Date: Fri 18 Nov 2011
Source: CDC. MMWR Morb Mortal Wkly Rep 2011; 60(45): 1554-6 [edited]
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6045a3.htm?s_cid=mm6045a3_w

Paralytic shellfish poisoning - southeast Alaska, May-June 2011
---------------------------------------------------------------
On 6 Jun 2011, the Section of Epidemiology (SOE) of the Alaska
Division of Public Health was notified of a case of paralytic
shellfish poisoning (PSP) in southeast Alaska. In collaboration with
local partners, SOE investigated and identified a total of 8 confirmed
and 13 probable PSP cases that occurred during May-June 2011. Warnings
to avoid noncommercially harvested shellfish were broadcast on local
radio and television and displayed at beaches and in post offices,
government offices, and businesses throughout the region. Commercially
harvested shellfish, which are tested for the presence of PSP-causing
toxins, were safe. Because the risk for PSP is unpredictable, persons
who consume noncommercially harvested Alaskan shellfish should know
that they are at risk for PSP, and suspected cases should be reported
promptly to SOE to initiate control measures in the affected area.

On 3 Jun 2011, a man aged 52 years residing in Metlakatla, on Annette
Island in southeast Alaska, awoke from a nap with numbness around his
mouth, tingling in his hands, and slight dyspnea. He was taken to the
Annette Island Service Unit, the community's health center, where a
clinician inquired about recent seafood consumption. After the man
reported eating a meal of steamed cockles shortly before his nap, the
clinician diagnosed PSP. The man was transported to Ketchikan where,
having become weak and unable to sit up in bed without assistance, he
was admitted to the intensive-care unit.

PSP primarily results from ingestion of saxitoxins, toxins produced by
marine dinoflagellate algae that accumulate in bivalve mollusks (such
as, butter clams, cockles, geoducks, and mussels) (1). PSP is a
potentially fatal neuroparalytic condition. Signs and symptoms of PSP
range from mild, short-lived paresthesias of the mouth or extremities
to severe, life-threatening paralysis (1). Because PSP is such a
serious condition and because a case indicates widespread risk to the
shellfish-consuming population of the affected area, immediate
reporting of PSP cases to SOE by health-care providers is mandatory in
Alaska.

When SOE was notified of the probable case of PSP (in patient A)
(Table - for table, see source URL above. - Mod.LL) on 6 Jun 2011,
they also were informed by a nurse in Metlakatla that other community
members had eaten cockles and had experienced PSP symptoms. That
afternoon, 2 SOE epidemiologists traveled to Metlakatla (population:
1460 persons) to investigate. The epidemiologists met with a visiting
public health nurse onsite and conducted active case finding by
broadcasting messages on local television and radio and through
word-of-mouth among community members.

For this investigation, a probable case of PSP was defined as a
compatible illness, including paresthesias, in a person shortly after
consumption of noncommercially harvested shellfish from Alaska waters
during spring 2011. A confirmed case also met this case definition and
had detectable saxitoxins in urine or levels 80 or more microg
saxitoxins/100 g of meat (the level at which product is considered
unsafe) in the shellfish that had been consumed before illness onset.

SOE identified an additional 12 probable cases in Metlakatla and used
a structured questionnaire for patient interviews. The team collected
shellfish from 2 beaches where shellfish associated with PSP had been
harvested. They also collected frozen cockles from a community member
who harvested them with the index patient (patient A) before that
patient became ill.

While conducting the investigation in Metlakatla, SOE was notified of
2 men working in Ketchikan (population: 8050 persons) who had been
examined in the hospital's emergency department on 8 Jun 2011 and
subsequently were admitted with symptoms consistent with PSP,
including paresthesias (patients F and G). Both patients were severely
ill; one had required intubation and assisted ventilation and was
admitted to the intensive-care unit. The men had shared a meal of
boiled, noncommercially harvested mussels. The hospital shipped
leftover mussels brought in by the men to the Alaska Department of
Environmental Conservation's Environmental Health Laboratory. Urine
specimens from the 2 hospitalized men and 2 persons who had
accompanied them to the hospital and had eaten the same meal of
mussels, but who had no symptoms themselves, were sent to CDC for
analysis (2). SOE requests that clinicians collect the 1st available
urine, freeze it immediately, and ship as soon as possible.

On 9 Jun 2011, the 2 SOE epidemiologists in Metlakatla traveled to
Ketchikan to interview patients F and G and conduct additional case
finding. While at the hospital in Ketchikan, the epidemiologists were
informed of 2 additional patients who had been examined in the
emergency department in May 2011 and who had been diagnosed with
shellfish allergies but who had symptoms consistent with PSP hours
after consuming a clam and cockle chowder. Active case finding in
Ketchikan identified 3 additional probable cases.

Overall, 8 probable and 5 confirmed PSP cases were identified in
Metlakatla, and 5 probable and 2 confirmed cases of PSP were
identified in Ketchikan during this outbreak. Another confirmed case
of PSP (in patient H) in Ketchikan had been reported to SOE in May
2011, for a total of 8 confirmed cases. In all, 21 cases of PSP were
identified in southeast Alaska during May-June 2011. All 21 patients
reported experiencing paresthesias, with incubation periods for all
cases ranging from 0 to 3.75 hours (median: 30 minutes). 4 of the 21
(19 percent) patients were hospitalized; none died. Of the 21
patients, 15 (71 percent) had consumed cockles; 4 (19 percent) had
consumed blue mussels; 1 (5 percent) had consumed butter clams and
cockles; and 1 (5 percent) had consumed clams that were otherwise
unspecified. 4 of the cases were reported to SOE, one after a delay of
3 days.

The cockles collected from the community member in Metlakatla and the
mussels collected from the hospital in Ketchikan tested positive for
high levels of saxitoxins (Table). Mussels collected from implicated
beaches in Metlakatla also tested positive for saxitoxin (range:
4602-5429 microg/100 g of meat).

[Reported by: McLaughlin JB, Fearey DA, Esposito TA, Porter KA]

MMWR Editorial note
--------------
The 21 cases of PSP identified in southeast Alaska during May-June
2011 represent a considerable increase in the numbers reported in
recent years (10 or less cases annually in Alaska since 1998).
However, this was not the 1st time an increase occurred in the annual
number of PSP cases in Alaska (3). Active case finding during this
outbreak enabled epidemiologists to identify persons with PSP symptoms
who had not sought care and thus would never have been reported. This
demonstrates that the overall burden of PSP in Alaska likely is
underestimated through standard reporting. However, saxitoxin levels
were reported to have been higher in shellfish in the region during
spring 2011 than in previous years (Kate Sullivan, University of
Alaska Southeast, personal communication, 2011), indicating that the
increase in the number of cases might not have been a surveillance
artifact.

PSP is a preventable condition. Avoidance of noncommercially harvested
Alaskan shellfish not tested for saxitoxins is the best way to prevent
PSP. Commercially harvested shellfish are tested for saxitoxin in
Alaska and considered safe for human consumption but shellfish
collected by persons for their own use are not. Because shellfish
harvesting is an important cultural tradition and shellfish are an
important subsistence food source for many Alaska Natives and other
Alaska residents, not everyone follows the public health
recommendation to avoid eating shellfish from noncommercial sources.
Furthermore, transient fish-processing workers in Alaska might be
unaware of the potential danger of eating untested Alaskan shellfish
because they are unfamiliar with PSP and might have limited English
literacy.

During the investigation, SOE epidemiologists posted signs at beaches
on Metlakatla and within the community to warn residents about the PSP
risks associated with consuming noncommercially harvested shellfish.
The warnings were printed in English, Tagalog, Russian, Spanish, and
Korean. The Ketchikan Public Health Center and the Alaska Department
of Fish and Game posted similar signs throughout Ketchikan and
surrounding areas. Additionally, the Alaska Department of Health and
Social Services issued press releases and conducted media interviews
to inform the public about the outbreak and the need to avoid
noncommercial harvesting of shellfish. No additional cases of PSP have
been reported in Alaska since this investigation.

Because Alaskan shellfish can have high levels of PSP saxitoxins at
any time of year and neither cooking nor freezing destroys the toxin,
development of a widely available, inexpensive, and easy-to-use test
kit to measure toxin concentrations in noncommercial shellfish would
be beneficial. Symptoms of PSP occur within minutes to hours of
shellfish consumption (1), and because the course of the illness is
unpredictable, immediate medical assessment is strongly recommended.
The roles of state and local governments, clinicians, and community
leaders include 1) identifying cases so that investigations and
control measures (such as, posting warning signs) can be initiated
promptly, 2) educating persons who choose to continue to consume
noncommercially harvested shellfish about the signs and symptoms of
PSP, and 3) recommending that medical care be sought immediately if
symptoms develop. Clinicians should report suspected cases of PSP to
local health authorities immediately and promptly collect and freeze
samples of patient urine and any uneaten shellfish for PSP toxin
testing.

References
----------
1. RaLonde R: Paralytic shellfish poisoning: the Alaska problem.
Alaska's Marine Resources 1996; 8(2): 1-7 [available at
http://seagrant.uaf.edu/features/PSP/PSP.pdf].
2. Johnson RC, Zhou Y, Statler K, et al: Quantification of saxitoxin
and neosaxitoxin in human urine utilizing isotope dilution tandem mass
spectrometry. J Anal Toxicol 2009; 33(1): 8-14 [abstract available at
http://www.ncbi.nlm.nih.gov/pubmed/19161664].
3. State of Alaska Section of Epidemiology; Alaska roulette --
paralytic shellfish poisoning, Ketchikan. State of Alaska Epidemiol
Bull 1982; 10 [available at
http://www.epi.alaska.gov/bulletins/docs/b1982_10.htm].

--
Communicated by:
ProMED-mail
<promed@promedmail.org>

[Metlakatla and Ketchikan in southeast Alaska can be located in the
HealthMap/ProMED-mail interactive map at
http://healthmap.org/r/1rAZ. - Sr.Tech.Ed.MJ]

[Paralytic shellfish poisoning (PSP)
(http://aquaticpath.umd.edu/toxalg/psp.html) is a significant
problem on both the east and west coasts of the USA. Caused by several
closely related species in the genus _Alexandrium_, PSP toxins are
responsible for persistent problems due to their accumulation in
filter feeding shellfish, but they also move through the food chain,
affecting zooplankton, fish larvae, adult fish, and even birds and
marine mammals. On the east coast, PSP is a serious and recurrent
problem from Maine to Massachusetts. Connecticut, Long Island (New
York), and New Jersey occasionally experience the toxin at low levels,
but these areas seem to define the southern extreme of this organism's
geographic distribution. On the west coast, PSP is a recurrent annual
problem along the coasts of northern California, Oregon, Washington,
and Alaska. Overall, PSP affects more coastline than any other harmful
algal bloom problem.

It is likely that seasonally recurring outbreaks of PSP are linked to
the existence of a dormant cyst stage in the _Alexandrium_ life
history. This strategy allows the species to deposit dormant cells in
sediments where they survive through harsh winter conditions and then
germinate to initiate new outbreaks in subsequent years. Prior to
1972, for example, PSP was restricted to the far eastern sections of
Maine ("down east") near the Canadian border. That year, however, a
massive red tide causing high levels of toxicity in those areas for
the 1st time recorded in history. Virtually every year since that
event, this region has experienced PSP outbreaks, a result of the
successful colonization of the area by _Alexandrium_ spp. A similar
expansion, with subsequent recurring outbreaks of _Alexandrium_,
occurred in the Puget Sound region of Washington in the late 1970's an
area with no prior history of shellfish poisoning. Long-term climatic
variability, which affects temperature, upwelling, and currents or
allows cysts to survive in areas where they did not before, may be
factors in such range extensions.

Shellfish that have caused this disease include mussels, cockles,
clams, scallops, oysters, crabs, and lobsters. Symptoms begin anywhere
from 15 minutes to 10 hours after eating the contaminated shellfish,
although usually within 2 hours. Symptoms are generally mild, and
begin with numbness or tingling of the face, arms, and legs. This is
followed by headache, dizziness, nausea, and muscular incoordination.
Patients sometimes describe a floating sensation. In cases of severe
poisoning, muscle paralysis and respiratory failure occur, and in
these cases death may occur in 2 to 25 hours. - Mod.LL]

See Also