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Swine Influenza A (H1N1) Infection in Two Children —
Southern California, March–April 2009
On April 17, 2009, CDC determined that two cases of febrile outpatient clinic, and a nasopharyngeal swab was collected for respiratory illness occurring in children who resided in adjacent testing as part of a clinical study. The boy received symptomatic counties in southern California were caused by infection with treatment, and all his symptoms resolved uneventfully within a swine influenza A (H1N1) virus. The viruses from the two approximately 1 week. The child had not received influenza cases are closely related genetically, resistant to amantadine vaccine during this influenza season. Initial testing at the clinic and rimantadine, and contain a unique combination of gene using an investigational diagnostic device identified an influ- segments that previously has not been reported among swine enza A virus, but the test was negative for human influenza or human influenza viruses in the United States or elsewhere. subtypes H1N1, H3N2, and H5N1. The San Diego County Neither child had contact with pigs; the source of the infection Health Department was notified, and per protocol, the speci- is unknown. Investigations to identify the source of infection men was sent for further confirmatory testing to reference labo- and to determine whether additional persons have been il from ratories, where the sample was verified to be an unsubtypable infection with similar swine influenza viruses are ongoing. This influenza A strain. On April 14, 2009, CDC received clinical report briefly describes the two cases and the investigations specimens and determined that the virus was swine influenza currently under way. Although this is not a new subtype of A (H1N1). The boy and his family reported that the child influenza A in humans, concern exists that this new strain of had had no exposure to pigs. Investigation of potential animal swine influenza A (H1N1) is substantial y different from human exposures among the boy’s contacts is continuing. The patient’s influenza A (H1N1) viruses, that a large proportion of the popu- mother had respiratory symptoms without fever in the first few lation might be susceptible to infection, and that the seasonal days of April 2009, and a brother aged 8 years had a respiratory influenza vaccine H1N1 strain might not provide protection. illness 2 weeks before illness onset in the patient and had a The lack of known exposure to pigs in the two cases increases second illness with cough, fever, and rhinorrhea on April 11, the possibility that human-to-human transmission of this new 2009. However, no respiratory specimens were collected from influenza virus has occurred. Clinicians should consider animal either the mother or brother during their acute illnesses. Public as well as seasonal influenza virus infections in their differential health officials are conducting case and contact investigations diagnosis of patients who have febrile respiratory illness and to determine whether illness has occurred among other rela- who 1) live in San Diego and Imperial counties or 2) traveled tives and contacts in California, and during the family’s travel to these counties or were in contact with il persons from these counties in the 7 days preceding their illness onset, or 3) had Patient B. CDC received an influenza specimen on April 17,
recent exposure to pigs. Clinicians who suspect swine influenza 2009, that had been forwarded as an unsubtypable influenza virus infections in a patient should obtain a respiratory specimen A virus from the Naval Health Research Center in San Diego, and contact their state or local health department to facilitate California. CDC identified this specimen as a swine influenza testing at a state public health laboratory.
A (H1N1) virus on April 17, 2009, and notified the California Department of Public Health. The source of the specimen, Case Reports
patient B, is a girl aged 9 years who resides in Imperial County, Patient A. On April 13, 2009, CDC was notified of a case
California, adjacent to San Diego County. On March 28, of respiratory illness in a boy aged 10 years who lives in San 2009, she had onset of cough and fever (104.3°F [40.2°C]). Diego County, California. The patient had onset of fever, She was taken to an outpatient facility that was participating cough, and vomiting on March 30, 2009. He was taken to an in an influenza surveillance project, treated with amoxicillin/ centers for disease control and prevention MMWR Dispatch
April 21, 2009
clavulanate potassium and an antihistamine, and has since influenza virus surveillance program to better understand the recovered uneventfully. The child had not received influenza epidemiology and ecology of swine influenza virus infections vaccine during this influenza season. The patient and her par- ents reported no exposure to pigs, although the girl did attend The viruses in these two patients demonstrate antiviral an agricultural fair where pigs were exhibited approximately resistance to amantadine and rimantadine, and testing to 4 weeks before illness onset. She reported that she did not see determine susceptibility to the neuraminidase inhibitor drugs pigs at the fair and went only to the amusement section of the oseltamivir and zanamivir is under way. Because these viruses fair. The Imperial County Public Health Department and the carry a unique combination of genes, no information currently California Department of Public Health are now conducting an is available regarding the efficiency of transmission in swine or investigation to determine possible sources of infection and to in humans. Investigations to understand transmission of this identify any additional human cases. The patient’s brother aged 13 years had influenza-like symptoms on April 1, 2009, and Reported by: M Ginsberg, MD, J Hopkins, MPH, A Maroufi, MPH,
a male cousin aged 13 years living in the home had influenza- G Dunne, DVM, DR Sunega, J Giessick, P McVay, MD, San Diego County Health and Human Svcs; K Lopez, MD, P Kriner, MPH, like symptoms on March 25, 2009, 3 days before onset of the K Lopez, S Munday, MD, Imperial County Public Health Dept; patient’s symptoms. The brother and cousin were not tested K Harriman, PhD, B Sun, DVM, G Chavez, MD, D Hatch, MD, for influenza at the time of their illnesses.
R Schechter, MD, D Vugia, MD, J Louie, MD, California Dept of Public Health. W Chung, MD, Dal as County Health and Human Svcs; Epidemiologic and Laboratory
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 Investigations
Center; J Tueller, MD, Navy Medical Center, San Diego, California. As of April 21, 2009, no epidemiologic link between patients T Gomez, DVM, Animal and Plant Health Inspection Svc, US Dept A and B had been identified, and no additional cases of infec- of Agriculture. F Averhoff, MD, F Alavrado-Ramy, MD, S Waterman, MD, J Neatherlin, MPH, Div of Global Migration and Quarantine; tion with the identified strain of swine influenza A (H1N1) L Finelli, DrPH, S Jain, MD, L Brammer, MPH, J Bresee, MD, had been identified. Surveillance data from Imperial and San C Bridges, MD, S Doshi, MD, R Donis, PhD, R Garten, PhD, J Katz, Diego counties, and from California overall, showed declin- PhD, S Klimov, PhD, D Jernigan, MD, S Lindstrom, PhD, B Shu, ing influenza activity at the time of the two patients’ illnesses. MD, T Uyeki, MD, X Xu, MD, N Cox, PhD, Influenza Div, National Case and contact investigations by the county and state Center for Infectious and Respiratory Diseases, CDC. departments of health in California and Texas are ongoing. Editorial Note: In the past, CDC has received reports of
Enhanced surveillance for possible additional cases is being approximately one human swine influenza virus infection every 1–2 years in the United States (2,3). However, during Preliminary genetic characterization of the influenza viruses December 2005–January 2009, 12 cases of human infection has identified them as swine influenza A (H1N1) viruses. The with swine influenza were reported; five of these 12 cases viruses are similar to each other, and the majority of their occurred in patients who had direct exposure to pigs, six in genes, including the hemagglutinin (HA) gene, are similar to patients reported being near pigs, and the exposure in one case those of swine influenza viruses that have circulated among was unknown (1,4,5). In the United States, novel influenza A U.S. pigs since approximately 1999; however, two genes cod- virus infections in humans, including swine influenza infec- ing for the neuraminidase (NA) and matrix (M) proteins are tions, have been nationally notifiable conditions since 2007. similar to corresponding genes of swine influenza viruses of the The recent increased reporting might be, in part, a result of Eurasian lineage (1). This particular genetic combination of increased influenza testing capabilities in public health labo- swine influenza virus segments has not been recognized previ- ratories, but genetic changes in swine influenza viruses and ously among swine or human isolates in the United States, or other factors also might be a factor (1,4,5). Although the vast elsewhere based on analyses of influenza genomic sequences majority of human infections with animal influenza viruses do available on GenBank.* Viruses with this combination of genes not result in human-to-human transmission (2,3), each case are not known to be circulating among swine in the United should be fully investigated to be certain that such viruses are States; however, no formal national surveil ance system exists to not spreading among humans and to limit further exposure determine what viruses are prevalent in the U.S. swine popula- of humans to infected animals, if infected animals are identi- tion. Recent collaboration between the U.S. Department of fied. Such investigations should include close collaboration Agriculture and CDC has led to development of a pilot swine between state and local public health officials with animal MMWR Dispatch
The lack of known exposure to pigs in the two cases described Interim guidance on infection control, treatment, and in this report increases the possibility that human-to-human chemoprophylaxis for swine influenza is available at transmission of this new influenza virus has occurred. Clinicians should consider animal as wel as seasonal influenza information about swine influenza is available at virus infections in the differential diagnosis of patients with febrile respiratory illness who live in San Diego and Imperial References
counties or have traveled to these areas or been in contact 1. Vincent AL, Ma W, Lager KM, Janke BH, Richt JA. Swine influenza with ill persons from these areas in the 7 days before their viruses: a North American perspective. Adv Virus Res 2008;72:127–54.
illness onset. In addition, clinicians should consider animal 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.
influenza infections among persons with febrile respiratory 3. Wells DL, Hopfensperger DJ, Arden NH, et al. Swine influenza virus il ness who have been near pigs, such as attending fairs or infections. Transmission from ill pigs to humans at a Wisconsin agricul- other places where pigs might be displayed. Clinicians who tural fair and subsequent probable person-to-person transmission. JAMA suspect swine influenza virus infections in humans should 4. Vincent AL, Swenson SL, Lager KM, Gauger PC, Loiacono C, Zhang Y. obtain a nasopharyngeal swab from the patient, place the swab Characterization of an influenza A virus isolated from pigs during an in a viral transport medium, and contact their state or local outbreak of respiratory disease in swine and people during a county fair in the United States. Vet Microbiol 2009;online publication ahead of health department to facilitate transport and timely diagnosis at a state public health laboratory. CDC requests that state 5. Newman AP, Reisdorf E, Beinemann J, et al. Human case of swine influ- public health laboratories send all influenza A specimens that enza A (H1N1) triple reassortant virus infection, Wisconsin. Emerg Infect cannot be subtyped to the CDC, Influenza Division, Virus Surveillance and Diagnostics Branch Laboratory.

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