Published Date: 2009-04-25 10:00:55
Subject: PRO/AH/EDR> Influenza A (H1N1) virus, swine, human - N America
Archive Number: 20090425.1552
INFLUENZA A (H1N1) VIRUS, SWINE, HUMAN - NORTH AMERICA
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
In this update:
 USA - MMWR
 USA, Mexico - WHO
 USA - MMWR
Date: 24 Apr 2009
Source: MMWR Morb Mortal Wkly Rep Dispatch 24 Apr 2009/58 (dispatch);1-3
Update: swine influenza A (H1N1) infections --- California and Texas, April
On [21 Apr 2009], CDC reported that 2 recent cases of febrile respiratory
illness in children in southern California had been caused by infection
with genetically similar swine influenza A (H1N1) viruses. The viruses
contained a unique combination of gene segments that had not been reported
previously among swine or human influenza viruses in the United States or
elsewhere (1). Neither child had known contact with pigs, resulting in
concern that human-to-human transmission might have occurred. The seasonal
influenza vaccine H1N1 strain is thought to be unlikely to provide
protection. This report updates the status of the ongoing investigation and
provides preliminary details about 6 additional persons infected by the
same strain of swine influenza A (H1N1) virus identified in the previous
cases, as of [24 Apr 2009]. The 6 additional cases were reported in San
Diego County, California (3 cases), Imperial County, California (one case),
and Guadalupe County, Texas (2 cases). CDC, the California Department of
Public Health, and the Texas Department of Health and Human Services are
conducting case investigations, monitoring for illness in contacts of the 8
patients, and enhancing surveillance to determine the extent of spread of
the virus. CDC continues to recommend that any influenza A viruses that
cannot be subtyped be sent promptly for testing to CDC. In addition, swine
influenza A (H1N1) viruses of the same strain as those in the US patients
have been confirmed by CDC among specimens from patients in Mexico.
Clinicians should consider swine influenza as well as seasonal influenza
virus infections in the differential diagnosis for patients who have
febrile respiratory illness and who 1) live in San Diego and Imperial
counties, California, or Guadalupe County, Texas, or traveled to these
counties or 2) who traveled recently to Mexico or were in contact with
persons who had febrile respiratory illness and were in one of the 3 US
counties or Mexico during the 7 days preceding their illness onset.
San Diego County, California. On [9 Apr 2009], an adolescent girl aged 16
years and her father aged 54 years went to a San Diego County clinic with
acute respiratory illness. The youth had onset of illness on [5 Apr 2009].
Her symptoms included fever, cough, headache, and rhinorrhea. The father
had onset of illness on [6 Apr 2009] with symptoms that included fever,
cough, and rhinorrhea. Both had self-limited illnesses and have recovered.
The father had received seasonal influenza vaccine in October 2008; the
daughter was unvaccinated. Respiratory specimens were obtained from both,
tested in the San Diego County Health Department Laboratory, and found to
be positive for influenza A using reverse transcription--polymerase chain
reaction (RT-PCR), but could not be further subtyped. Two household
contacts of the patients have reported recent mild acute respiratory
illnesses; specimens have been collected from these household members for
testing. One additional case, in a child residing in San Diego County, was
identified on [24 Apr 2009]; epidemiologic details regarding this case are
Imperial County, California. A woman aged 41 years with an autoimmune
illness who resided in Imperial County developed fever, headache, sore
throat, diarrhea, vomiting, and myalgias on [12 Apr 2009]. She was
hospitalized on [15 Apr 2009]. She recovered and was discharged on [22 Apr
2009]. A respiratory specimen obtained [16 Apr 2009] was found to be
influenza A positive by RT-PCR at the San Diego Country Health Department
Laboratory, but could not be further subtyped. The woman had not been
vaccinated against seasonal influenza viruses during the 2008--09 season.
Three household contacts of the woman reported no recent respiratory illness.
Guadalupe County, Texas. Two adolescent boys aged 16 years who resided in
Guadalupe County near San Antonio were tested for influenza and found to be
positive for influenza A on [15 Apr 2009]. The youths had become ill with
acute respiratory symptoms on [10 Apr 2009] and [14 Apr 2009],
respectively, and both had gone to an outpatient clinic for evaluation on
[15 Apr 2009]. Identification and tracking of the youths' contacts is under
Five of the new cases were identified through diagnostic specimens
collected by the health care facility in which the patients were examined,
based on clinical suspicion of influenza; information regarding the 6th
case is pending. The positive specimens were sent to public health
laboratories for further evaluation as part of routine influenza
surveillance in the 3 counties.
Outbreaks in Mexico
Mexican public health authorities have reported increased levels of
respiratory disease, including reports of severe pneumonia cases and
deaths, in recent weeks. Most reported disease and outbreaks are reported
from central Mexico, but outbreaks and severe respiratory disease cases
also have been reported from states along the US-Mexico border. Testing of
specimens collected from persons with respiratory disease in Mexico by the
CDC laboratory has identified the same strain of swine influenza A (H1N1)
as identified in the US cases. However, no clear data are available to
assess the link between the increased disease reports in Mexico and the
confirmation of swine influenza in a small number of specimens. CDC is
assisting public health authorities in Mexico in testing additional
specimens and providing epidemiologic support. None of the US patients
traveled to Mexico within 7 days of the onset of their illness.
Epidemiologic and laboratory investigations
As of April 24, epidemiologic links identified among the new cases included
1) the household of the father and daughter in San Diego County, and 2) the
school attended by the 2 youths in Guadalupe County. As of April 24, no
epidemiologic link between the Texas cases and the California cases had
been identified, nor between the 3 new California cases and the 2 cases
previously reported. No recent exposure to pigs has been identified for any
of the 7 patients. Close contacts of all patients are being investigated to
determine whether person-to-person spread has occurred.
Enhanced surveillance for additional cases is ongoing in California and in
Texas. Clinicians have been advised to test patients who visit a clinic or
hospital with febrile respiratory illness for influenza. Positive samples
should be sent to public health laboratories for further characterization.
Seasonal influenza activity continues to decline in the United States,
including in Texas and California, but remains a cause of influenza-like
illness in both areas.
Viruses from 6 of the 8 patients have been tested for resistance to
antiviral medications. All 6 have been found resistant to amantadine and
rimantidine but sensitive to zanamivir and oseltamivir.
Reported by: San Diego County Health and Human Svcs; Imperial County Public
Health Dept; California Dept of Public Health. Dallas County Health and
Human Svcs; Texas Dept of State Health Svcs. Naval Health Research Center;
Navy Medical Center, San Diego, California. Animal and Plant Health
Inspection Svc, US Dept of Agriculture. Div of Global Migration and
Quarantine, National Center for Preparedness, Detection, and Control of
Infectious Diseases; National Center for Zoonotic, Vector-Borne, and
Enteric Diseases; Influenza Div, National Center for Infectious and
Respiratory Diseases, CDC.
In the US, novel influenza A virus infections in humans, including swine
influenza A (H1N1) infections, have been nationally notifiable conditions
since 2007. Recent pandemic influenza preparedness activities have greatly
increased the capacity of public health laboratories in the US to perform
RT-PCR for influenza and to subtype influenza A viruses they receive from
their routine surveillance, enhancing the ability of US laboratories to
identify novel influenza A virus infections. Before the cases described in
this ongoing investigation, recent cases of swine influenza in humans
reported to CDC occurred in persons who either had exposure to pigs or to a
family member with exposure to pigs. Transmission of swine influenza
viruses between persons with no pig exposure has been described previously,
but that transmission has been limited (2,3). The lack of a known history
of pig exposure for any of the patients in the current cases indicates that
they acquired infection through contact with other infected persons.
The spectrum of illness in the current cases is not yet fully defined. In
the 8 cases identified to date, 6 patients had self-limited illnesses and
were treated as outpatients. One patient was hospitalized. Previous reports
of swine influenza, although in strains different from the one identified
in the current cases, mostly included mild upper respiratory illness; but
severe lower respiratory illness and death also have been reported (2,3).
The extent of spread of the strain of swine influenza virus in this
investigation is not known. Ongoing investigations by California and Texas
authorities of the 2 previously reported patients, a boy aged 10 years and
a girl aged 9 years, include identification of persons in close contact
with the children during the period when they were likely infectious
(defined as from 1 day before symptom onset to 7 days after symptom onset).
These contacts have included household members, extended family members,
clinic staff members who cared for the children, and persons in close
contact with the boy during his travel to Texas on April 3. Respiratory
specimens are being collected from contacts found to have ongoing illness.
In addition, enhanced surveillance for possible cases is under way in
clinics and hospitals in the areas where the patients reside. Similar
investigations and enhanced surveillance are now under way in the
additional 6 cases.
Clinicians should consider swine influenza infection in the differential
diagnosis of patients with febrile respiratory illness and who 1) live in
San Diego and Imperial counties, California, or Guadalupe County, Texas, or
traveled to these counties or 2) who traveled recently to Mexico or were in
contact with persons who had febrile respiratory illness and were in one of
the 3 US counties or Mexico during the 7 days preceding their illness
onset. Any unusual clusters of febrile respiratory illness elsewhere in the
United States also should be investigated.
Patients who meet these criteria should be tested for influenza, and
specimens positive for influenza should be sent to public health
laboratories for further characterization. Clinicians who suspect swine
influenza virus infections in humans should obtain a nasopharyngeal swab
from the patient, place the swab in a viral transport medium, refrigerate
the specimen, and then contact their state or local health department to
facilitate transport and timely diagnosis at a state public health
laboratory. CDC requests that state public health laboratories promptly
send all influenza A specimens that cannot be subtyped to the CDC,
Influenza Division, Virus Surveillance and Diagnostics Branch Laboratory.
As a precautionary step, CDC is working with other partners to develop a
vaccine seed strain specific to these recent swine influenza viruses in humans.
As always, persons with febrile respiratory illness should stay home from
work or school to avoid spreading infections (including influenza and other
respiratory illnesses) to others in their communities. In addition,
frequent hand washing can lessen the spread of respiratory illness (5).
Interim guidance on infection control, treatment, and chemoprophylaxis for
swine influenza is available at
<http://www.cdc.gov/flu/swine/recommendations.htm>. Additional information
about swine influenza is available at <http://www.cdc.gov/flu/swine/index.htm>.
1. CDC. Swine influenza A (H1N1) infection in two children -- Southern
California, March-April 2009. MMWR 2009; 58: 400-2. [available at
2. Myers KP, Olsen CW, Gray GC. Cases of swine influenza in humans: a
review of the literature. Clin Infect Dis 2007; 44: 1084-8.
3. Wells DL, Hopfensperger DJ, Arden NH, et al. Swine influenza virus
infections. Transmission from ill pigs to humans at a Wisconsin
agricultural fair and subsequent probable person-to-person transmission.
JAMA 1991; 265: 478-81.
4. Newman AP, Reisdorf E, Beinemann J, et al. Human case of swine influenza
A (H1N1) triple reassortant virus infection, Wisconsin. Emerg Infect Dis
2008; 14: 1470-2.
5. Ryan MA, Christian RS, Wohlrabe J. Handwashing and respiratory illness
among young adults in military training. Am J Prev Med 2001; 21: 79-83.
 USA, Mexico - WHO
Date: 24 Apr 2009
Source: WHO Epidemic and Pandemic Alert and Response (EPR) [edited]
Influenza-like illness in the United States and Mexico 24 April 2009
The United States Government has reported 7 confirmed human cases of swine
influenza A/H1N1 in the USA (5 in California and 2 in Texas) and 9 suspect
cases. All 7 confirmed cases had mild influenza-like illness (ILI), with
only one requiring brief hospitalization. No deaths have been reported.
The Government of Mexico has reported three separate events. In the Federal
District of Mexico, surveillance began picking up cases of ILI starting 18
March . The number of cases has risen steadily through April and as
of 23 April there are now more than 854 cases of pneumonia from the
capital, 59 of whom have died. In San Luis Potosi, in central Mexico, 24
cases of ILI, with 3 deaths, have been reported. And from Mexicali, near
the border with the United States, 4 cases of ILI, none fatal, have been
Of the Mexican cases, 18 have been laboratory confirmed in Canada as swine
influenza A/H1N1, while 12 of those are genetically identical to the swine
influenza A/H1N1 viruses from California.
The majority of these cases have occurred in otherwise healthy young
adults. Influenza normally affects the very young and the very old, but
these age groups have not been heavily affected in Mexico. Because there
are human cases associated with an animal influenza virus, and because of
the geographical spread of multiple community outbreaks, plus the somewhat
unusual age groups affected, these events are of high concern.
The swine influenza A/H1N1 viruses characterized in this outbreak have not
been previously detected in pigs or humans. The viruses so far
characterized have been sensitive to oseltamivir, but resistant to both
amantadine and rimantadine.
The World Health Organization has been in constant contact with the health
authorities in the United States, Mexico, and Canada in order to better
understand the risk which these ILI events pose. WHO (and the Pan American
Health Organization [PAHO]) is sending missions of experts to Mexico to
work with health authorities there. It is helping its member states to
increase field epidemiology activities, laboratory diagnosis and clinical
management. Moreover, WHO's partners in the Global Alert and Response
Network have been alerted and are ready to assist as requested by the
WHO acknowledges the US and Mexico for their proactive reporting and their
collaboration with WHO and will continue to work with member states to
further characterize the outbreak.
 Mexico - Newswire
Date: 24 Apr 2009
Source: Yahoo News / Associated Press
A unique strain of swine flu is the suspected killer of dozens of people in
Mexico, where authorities closed schools, museums, libraries and theaters
in the capital on Friday [24 Apr 2009] to try to contain an outbreak that
has spurred concerns of a global flu epidemic.
The worrisome new virus -- which combines genetic material from pigs, birds
and humans in a way researchers have not seen before -- also sickened at
least eight people in Texas and California, though there have been no
deaths in the US "We are very, very concerned," WHO spokesman Thomas
Abraham said. "We have what appears to be a novel virus and it has spread
from human to human ... It's all hands on deck at the moment."
The outbreak caused alarm in Mexico, where more than 1000 people have been
sickened. Residents of the capital donned surgical masks and authorities
ordered the most sweeping shutdown of public gathering places in a quarter
century. President Felipe Calderon met with his Cabinet Friday [24 Apr
2009] to coordinate Mexico's response.
WHO was convening an expert panel to consider whether to raise the pandemic
alert level or issue travel advisories. It might already be too late to
contain the outbreak, a prominent US pandemic flu expert said late on Friday.
Given how quickly flu can spread around the globe, if these are the first
signs of a pandemic, then there are probably cases incubating around the
world already, said Dr Michael Osterholm at the University of Minnesota.
In Mexico City, "literally hundreds and thousands of travelers come in and
out every day," Osterholm said. "You'd have to believe there's been more
unrecognized transmission that's occurred."
There is no vaccine that specifically protects against swine flu, and it
was unclear how much protection current human flu vaccines might offer. A
"seed stock" genetically matched to the new swine flu virus has been
created by the US Centers for Disease Control, said Dr Richard Besser, the
agency's acting director. If the government decides vaccine production is
necessary, manufacturers would need that stock to get started.
Authorities in Mexico urged people to avoid hospitals unless they had a
medical emergency, since hospitals are centers of infection. They also said
Mexicans should refrain from customary greetings such as shaking hands or
kissing cheeks. At Mexico City's international airport, passengers were
questioned to try to prevent anyone with flu symptoms from boarding
airplanes and spreading the disease.
Epidemiologists are particularly concerned because the only fatalities so
far were in young people and adults. The 8 US victims recovered from
symptoms that were like those of the regular flu, mostly fever, cough, and
sore throat, though some also experienced vomiting and diarrhea.
US health officials announced an outbreak notice to travelers, urging
caution and frequent handwashing, but stopping short of telling Americans
to avoid Mexico.
Mexico's health secretary Jose Angel Cordoba said 68 people have died of
flu and the new swine flu strain had been confirmed in 20 of those deaths.
At least 1004 people nationwide were sick from the suspected flu, he said.
The geographical spread of the outbreaks also concerned the WHO -- while 13
of the 20 deaths were in Mexico City, the rest were spread across Mexico --
4 in central San Luis Potosi, 2 up near the US border in Baja California,
and one in southern Oaxaca state.
Scientists have long been concerned that a new flu virus could launch a
worldwide pandemic of a killer disease. A new virus could evolve when
different flu viruses infect a pig, a person or a bird, mingling their
genetic material. The resulting hybrid could spread quickly because people
would have no natural defenses against it.
Still, flu experts were concerned but not alarmed about the latest
outbreak. "We've seen swine influenza in humans over the past several
years, and in most cases, it's come from direct pig contact. This seems to
be different," said Dr Arnold Monto, a flu expert with the University of
Michigan. "I think we need to be careful and not apprehensive, but
certainly paying attention to new developments as they proceed."
CDC says 2 flu drugs, Tamiflu [oseltamivir] and Relenza [zanamivir], seem
effective against the new strain. Roche, the maker of Tamiflu, said the
company is prepared to immediately deploy a stockpile of the drug if
requested. Both drugs must be taken early, within a few days of the onset
of symptoms, to be most effective. Cordoba said Mexico has enough Tamiflu
to treat 1 million people, but the medicine will be strictly controlled and
handed out only by doctors.
Mexico's government had maintained until late on Thursday that there was
nothing unusual about the flu cases, although this year's flu season had
been worse and longer than past years. The sudden turnaround by public
health officials angered many Mexicans. The city was handing out free
surgical masks to passengers on buses and the subway system, which carries
5 million people each day. Government workers were ordered to wear the
masks, and authorities urged residents to stay home from work if they felt ill.
Closing schools across Mexico's capital of 20 million kept 6.1 million
students home, as well as thousands of university students. All state and
city-run cultural activities were suspended, including libraries, state-run
theaters, and at least 14 museums. Private athletic clubs closed down and
soccer leagues were considering canceling weekend games. The closures were
the first citywide shutdown of public gathering places since millions died
in the devastating 1985 earthquake.
Mexico's response brought to mind other major outbreaks, such as when SARS
hit Asia. At its peak in 2003, Beijing shuttered schools, cinemas and
restaurants, and thousands of people were quarantined at home. In March
2008, Hong Kong ordered more than half a million students to stay home for
2 weeks because of a flu outbreak. It was the first such closure in Hong
Kong since the outbreak of SARS, or severe acute respiratory syndrome.
"It's great they are taking precautions," said Lillian Molina, a teacher at
the Montessori's World preschool in Mexico City, who scrubbed down empty
classrooms with Clorox, soap and Lysol between fielding calls from worried
US health officials said the outbreak is not yet a reason for alarm in the
United States. The 5 people sickened in California and 3 in Texas have all
recovered. It's unclear how the 8, who became ill between late March and
mid-April, contracted the virus because none were in contact with pigs,
which is how people usually catch swine flu. And only a few were in contact
with each other.
CDC officials described the virus as having a unique combination of gene
segments not seen before in people or pigs. The bug contains human virus,
avian virus from North America and pig viruses from North America, Europe,
and Asia. It may be completely new, or it may have been around for a while
and was only detected now through improved testing and surveillance, CDC
The most notorious flu pandemic is thought to have killed at least 40
million people worldwide in 1918-19. Two other, less deadly flu pandemics
struck in 1957 and 1968.
[byline: Mark Stevenson]
[ProMED-mail would like to thank all our subscribers who have been
submitting numerous information sources on the above outbreak(s) situation
that is unfolding by the hour as more and more information becomes available.
According to the above information are now 8 confirmed cases of the novel
influenza A H1N1 virus infection in the USA, all mild, occurring in
counties with known increased population flow/transit between the USA &
Mexico. According to the official report from WHO, there have been now more
than 854 cases of pneumonia reported from the capital (Mexico City) of
which 59 have died (case fatality rate [CFR] 6.9 per cent). In San Luis
Potosi (central Mexico) there were 24 cases of influenza-like illness (ILI)
reported with 3 deaths (CFR 12.5 per cent) and in Mexicali, (near the
border with the United States), there have been 4 cases of ILI reported
with no deaths.
It should be noted here that the data from Mexico refers to inpatient
hospitalized cases, whereas the ILI surveillance sites in the USA are
predominantly from sentinel reporting outpatient facilities. This
difference in surveillance sites may account for an apparent disparity in
severity of the illnesses in cases reported in Mexico vs those presently
reported in the USA. As more uniform active surveillance (case finding) is
implemented, these disparities may lessen.
The absence of direct connection between the cases in the USA and the cases
in Mexico does not rule out the outbreaks being linked, as the population
flow between the 2 countries is high and 12 isolates from Mexico are
reported to be genetically identical to those isolated in the USA. One
suspects the epidemic curve is already multiple generations past the "index
case". The virus has apparently been circulating in Mexico for several
weeks, and in the USA for at least 2 weeks according to the above reports.
We should call it swine flu as this is common parlance but there have been
no cases in swine to date. We don't know if this strain has occurred in
swine but there is no evidence that it has. No surveillance yet but the SIV
(swine influenza virus) is endemic and controlled by vaccination here in
the US and probably in Mexico. Mexico's pork production is just like that
in the US, Canada and Europe -- very intensive. I do not know about the
extent of backyard swine but will try to find out. - Mod.PC
The map link shows the proximity of Texas, California, and Mexico
<http://healthmap.org/promed/en?v=24,-102.5,5> - Mod.SH]