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A ProMED-mail post
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International Society for Infectious Diseases
Date: Wed 21 Apr 2009
Source: CDC. MMWR Morb Mortal Wkly Rep 2009; 58 (dispatch): 1-3 [edited]
Swine influenza A (H1N1) infection in 2 children - southern California,
March/April 2009
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On 17 Apr 2009, CDC determined that 2 cases of febrile respiratory illness
occurring in children who resided in adjacent counties in southern
California were caused by infection with a swine influenza A (H1N1) virus.
The viruses from the 2 cases are closely related genetically, resistant to
amantadine and rimantadine, and contain a unique combination of gene
segments that previously has not been reported among swine or human
influenza viruses in the United States or elsewhere. Neither child had
contact with pigs; the source of the infection is unknown. Investigations
to identify the source of infection and to determine whether additional
persons have been ill from infection with similar swine influenza viruses
are ongoing. This report briefly describes the 2 cases and the
investigations currently under way. Although this is not a new subtype of
influenza A in humans, concern exists that this new strain of swine
influenza A (H1N1) is substantially different from human influenza A (H1N1)
viruses, that a large proportion of the population might be susceptible to
infection, and that the seasonal influenza vaccine H1N1 strain might not
provide protection. The lack of known exposure to pigs in the 2 cases
increases the possibility that human-to-human transmission of this new
influenza virus has occurred. Clinicians should consider animal as well as
seasonal influenza virus infections in their differential diagnosis of
patients who have febrile respiratory illness and who 1) live in San Diego
and Imperial counties or 2) traveled to these counties or were in contact
with ill persons from these counties in the 7 days preceding their illness
onset, or 3) had recent exposure to pigs. Clinicians who suspect swine
influenza virus infections in a patient should obtain a respiratory
specimen and contact their state or local health department to facilitate
testing at a state public health laboratory.
Case reports
------------
Patient A. On 13 Apr 2009, CDC was notified of a case of respiratory
illness in a boy aged 10 years who lives in San Diego County, California.
The patient had onset of fever, cough, and vomiting on 30 Mar 2009. He was
taken to an outpatient clinic, and a nasopharyngeal swab was collected for
testing as part of a clinical study. The boy received symptomatic
treatment, and all his symptoms resolved uneventfully within approximately
one week. The child had not received influenza vaccine during this
influenza season. Initial testing at the clinic using an investigational
diagnostic device identified an influenza A virus, but the test was
negative for human influenza subtypes H1N1, H3N2, and H5N1. The San Diego
County Health Department was notified, and per protocol, the specimen was
sent for further confirmatory testing to reference laboratories, where the
sample was verified to be an unsubtypable influenza A strain. On 14 Apr
2009, CDC received clinical specimens and determined that the virus was
swine influenza A (H1N1). The boy and his family reported that the child
had had no exposure to pigs. Investigation of potential animal exposures
among the boy's contacts is continuing. The patient's mother had
respiratory symptoms without fever in the 1st few days of April 2009, and a
brother aged 8 years had a respiratory illness 2 weeks before illness onset
in the patient and had a 2nd illness with cough, fever, and rhinorrhea on
11 Apr 2009. However, no respiratory specimens were collected from either
the mother or brother during their acute illnesses. Public health officials
are conducting case and contact investigations to determine whether illness
has occurred among other relatives and contacts in California, and during
the family's travel to Texas on 3 Apr 2009.
Patient B. CDC received an influenza specimen on 17 Apr 2009, which had
been forwarded as an unsubtypable influenza A virus from the Naval Health
Research Center in San Diego, California. CDC identified this specimen as a
swine influenza A (H1N1) virus on 17 Apr 2009, and notified the California
Department of Public Health. The source of the specimen, patient B, is a
girl aged 9 years who resides in Imperial County, California, adjacent to
San Diego County. On 28 Mar 2009, she had onset of cough and fever (104.3
deg F [40.2 deg C]). She was taken to an outpatient facility that was
participating in an influenza surveillance project, treated with
amoxicillin/clavulanate potassium and an antihistamine, and has since
recovered uneventfully. The child had not received influenza vaccine during
this influenza season. The patient and her parents reported no exposure to
pigs, although the girl did attend an agricultural fair where pigs were
exhibited approximately 4 weeks before illness onset. She reported that she
did not see pigs at the fair and went only to the amusement section of the
fair. The Imperial County Public Health Department and the California
Department of Public Health are now conducting an investigation to
determine possible sources of infection and to identify any additional
human cases. The patient's brother aged 13 years had influenza-like
symptoms on 1 Apr 2009, and a male cousin aged 13 years living in the home
had influenza-like symptoms on 25 Mar 2009, 3 days before onset of the
patient's symptoms. The brother and cousin were not tested for influenza at
the time of their illnesses.
Epidemiologic and laboratory investigations
-------------------------------------------
As of 21 Apr 2009, no epidemiologic link between patients A and B had been
identified, and no additional cases of infection with the identified strain
of swine influenza A (H1N1) had been identified. Surveillance data from
Imperial and San Diego counties, and from California overall, showed
declining influenza activity at the time of the 2 patients' illnesses. Case
and contact investigations by the county and state departments of health in
California and Texas are ongoing. Enhanced surveillance for possible
additional cases is being implemented in the area.
Preliminary genetic characterization of the influenza viruses has
identified them as swine influenza A (H1N1) viruses. The viruses are
similar to each other, and the majority of their genes, including the
hemagglutinin (HA) gene, are similar to those of swine influenza viruses
that have circulated among US pigs since approximately 1999; however, 2
genes coding for the neuraminidase (NA) and matrix (M) proteins are similar
to corresponding genes of swine influenza viruses of the Eurasian lineage
(1). This particular genetic combination of swine influenza virus segments
has not been recognized previously among swine or human isolates in the
United States, or elsewhere based on analyses of influenza genomic
sequences available on GenBank. Viruses with this combination of genes are
not known to be circulating among swine in the United States; however, no
formal national surveillance system exists to determine what viruses are
prevalent in the US swine population. Recent collaboration between the US
Department of Agriculture and CDC has led to development of a pilot swine
influenza virus surveillance program to better understand the epidemiology
and ecology of swine influenza virus infections in swine and humans.
The viruses in these 2 patients demonstrate antiviral resistance to
amantadine and rimantadine, and testing to determine susceptibility to the
neuraminidase inhibitor drugs oseltamivir and zanamivir is under way.
Because these viruses carry a unique combination of genes, no information
currently is available regarding the efficiency of transmission in swine or
in humans. Investigations to understand transmission of this virus are ongoing.
[Reported by: M Ginsberg, MD, J Hopkins, MPH, A Maroufi, MPH, G Dunne, DVM,
DR Sunega, J Giessick, P McVay, MD, San Diego County Health and Human Svcs;
K Lopez, MD, P Kriner, MPH, K Lopez, S Munday, MD, Imperial County Public
Health Dept; K Harriman, PhD, B Sun, DVM, G Chavez, MD, D Hatch, MD, R
Schechter, MD, D Vugia, MD, J Louie, MD, California Dept of Public Health.
W Chung, MD, Dallas County Health and Human Svcs; N Pascoe, S Penfield, MD,
J Zoretic, MD, V Fonseca, MD, Texas Dept of State Health Svcs. P Blair,
PhD, D Faix, PhD, Naval Health Research Center; J Tueller, MD, Navy Medical
Center, San Diego, California. T Gomez, DVM, Animal and Plant Health
Inspection Svc, US Dept of Agriculture. F Averhoff, MD, F Alavrado-Ramy,
MD, S Waterman, MD, J Neatherlin, MPH, Div of Global Migration and
Quarantine; L Finelli, DrPH, S Jain, MD, L Brammer, MPH, J Bresee, MD, C
Bridges, MD, S Doshi, MD, R Donis, PhD, R Garten, PhD, J Katz, PhD, S
Klimov, PhD, D Jernigan, MD, S Lindstrom, PhD, B Shu, MD, T Uyeki, MD, X
Xu, MD, N Cox, PhD, Influenza Div, National Center for Infectious and
Respiratory Diseases, CDC.]
MMWR editorial note
-------------------
In the past, CDC has received reports of approximately one human swine
influenza virus infection every 1-2 years in the United States (2,3).
However, during December 2005-January 2009, 12 cases of human infection
with swine influenza were reported; 5 of these 12 cases occurred in
patients who had direct exposure to pigs, 6 in patients reported being near
pigs, and the exposure in one case was unknown (1,4,5). In the United
States, novel influenza A virus infections in humans, including swine
influenza infections, have been nationally notifiable conditions since
2007. The recent increased reporting might be, in part, a result of
increased influenza testing capabilities in public health laboratories, but
genetic changes in swine influenza viruses and other factors also might be
a factor (1,4,5). Although the vast majority of human infections with
animal influenza viruses do not result in human-to-human transmission
(2,3), each case should be fully investigated to be certain that such
viruses are not spreading among humans and to limit further exposure of
humans to infected animals, if infected animals are identified. Such
investigations should include close collaboration between state and local
public health officials with animal health officials.
The lack of known exposure to pigs in the 2 cases described in this report
increases the possibility that human-to-human transmission of this new
influenza virus has occurred. Clinicians should consider animal as well as
seasonal influenza virus infections in the differential diagnosis of
patients with febrile respiratory illness who live in San Diego and
Imperial counties or have traveled to these areas or been in contact with
ill persons from these areas in the 7 days before their illness onset. In
addition, clinicians should consider animal influenza infections among
persons with febrile respiratory illness who have been near pigs, such as
attending fairs or other places where pigs might be displayed. 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, and 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 send all influenza A
specimens that cannot be subtyped to the CDC, Influenza Division, Virus
Surveillance and Diagnostics Branch Laboratory.
Interim guidance on infection control, treatment, and chemoprophylaxis for
swine influenza is available at
about swine influenza is available at
References
----------
1. Vincent AL, Ma W, Lager KM, et al. Swine influenza viruses: a North
American perspective. Adv Virus Res 2008; 72: 127-54 [abstract 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 [abstract
available at
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 [abstract available at
4. Vincent AL, Swenson SL, Lager KM, et al. Characterization of an
influenza A virus isolated from pigs during an outbreak of respiratory
disease in swine and people during a county fair in the United States. Vet
Microbiol 2009; online publication ahead of print [abstract available at
5. 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 [available at
--
communicated by:
ProMED-mail
[Infection with swine influenza virus has been detected sporadically in
humans since the 1950s and the human disease is usually clinically similar
to disease caused by infections with human influenza viruses. However,
complications that include pneumonia and death have occasionally been
reported in the literature in otherwise healthy adults without underlying
disease. On the whole, human infections with swine influenza virus, to
date, have been different and much milder than those seen with avian
influenza A (H5N1) and more similar to infections with low pathogenic avian
influenza viruses (see Eurosurveillance edition 2009; 14(7) at
The significant features of this report are that although this is not a new
subtype of influenza A in humans, concerns exist that this new strain of
swine influenza A (H1N1) is substantially different from human influenza A
(H1N1) viruses, that a large proportion of the population might be
susceptible to infection, and that the seasonal influenza vaccine H1N1
strain might not provide protection. The lack of known exposure to pigs in
the 2 cases increases the possibility that human-to-human transmission of
this new influenza virus has occurred.
The viruses isolated from the 2 children are similar and carry a unique
combination of genes not previously encountered. No information currently
is available regarding the efficiency of their transmission in swine or in
humans - Mod.CP
San Diego and Imperial are the southernmost counties in California and can
be located on the map at
of California can be seen on the HealthMap/ProMED-mail interactive map at
[see also:
Influenza A (H1N1) virus, swine, human - Spain 20090220.0715
2008
---
Influenza A (H1N1) virus, swine, human - USA (TX) 20081125.3715
2007
---
Influenza A (H2N3) virus, swine - USA 20071219.4079
2006
---
Influenza, swine, human - USA (IA): November 2006 20070108.0077]
.................cp/mj/sh
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