Published Date: 2012-10-04 15:54:41
Subject: PRO/EDR> Influenza (97): USA & worldwide, CDC update
Archive Number: 20121004.1324516

INFLUENZA (97): USA AND WORLDWIDE, CDC UPDATE
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Date: Fri 5 Oct 2012
Source: MMWR Weekly 61(39);785-789 [edited]
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6139a1.htm?s_cid=mm6139a1_e


During the period 20 May to 22 Sep 2012, the United States experienced low levels of seasonal influenza activity overall; however, more seasonal influenza viruses were detected than in the summer months of previous years. Influenza A (H1N1)pdm09 (pH1N1), influenza A (H3N2), and influenza B viruses were detected worldwide and were identified sporadically in the United States. In July 2012, influenza A (H3N2) variant viruses (H3N2v) were 1st detected in Indiana, and since 12 Jul 2012, a total of 306 cases have been reported from 10 states. This report summarizes influenza activity in the United States and worldwide since 20 May 2012.

United States
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During the period 20 May to 22 Sep 2012, U.S. WHO and NREVSS [the National Respiratory and Enteric Virus Surveillance System] collaborating laboratories tested 42 562 respiratory specimens for influenza viruses; 2986 (7.0 percent) tested positive for influenza, indicating higher levels of activity than typically seen in summer months but lower levels than during winter months and the height of influenza virus circulation. During the summer months of the previous 6 years (excluding the summer during the 2009 pandemic), the average number of respiratory specimens tested for influenza was 29 728 (range: 20 652-39 523), with an average of 375 (1.3 percent) specimens testing positive (range: 245-541). Of the 2986 specimens positive for influenza in the summer months of 2012, a total of 1497 (50 percent) were influenza A viruses, and 1489 (50 percent) were influenza B viruses. Influenza B viruses predominated and were reported more frequently than influenza A viruses from May until mid-July 2012; influenza A (H3N2) viruses were more commonly reported from mid-July to September 2012. Of the influenza A viruses, 1117 (75 percent) were subtyped: 759 (68 percent) were influenza A (H3N2) viruses, 263 (24 percent) were H3N2v viruses, and 95 (9 percent) were pH1N1 viruses. Influenza viruses were reported from 44 states and Puerto Rico in all 10 U.S. Department of Health and Human Services (HHS) Regions. The largest proportion of positive samples came from the southeastern United States (HHS Region 4: Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, and Tennessee) with 1133 (38 percent), followed by western states (HHS Region 9: Arizona, California, Hawaii, and Nevada) with 726 (24 percent).

During 22 May to 22 Sep 2012, data from ILINet indicated that the weekly percentage of outpatient visits to ILINet [Outpatient Influenza-like Illness Surveillance Network] providers for influenza-like illness (ILI) remained below the national baseline of 2.4 percent and ranged from 0.9 percent to 1.3 percent. The percentage of deaths attributed to pneumonia and influenza (P&I), as reported by the 122 Cities Mortality Reporting System, remained below the epidemic threshold and ranged from 5.5 percent to 6.6 percent. Two influenza-associated pediatric deaths were reported; one was associated with an influenza B virus, and one was associated with a pH1N1 virus.

Novel Influenza A Virus Infection
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During 12 May to 22 Sep 2012, 306 cases of H3N2v virus were reported from 10 states (Hawaii [one], Illinois [4], Indiana [138], Maryland [12], Michigan [6], Minnesota [4], Ohio [107], Pennsylvania [11], West Virginia [3], and Wisconsin [20]), with 16 H3N2v-associated hospitalizations and one H3N2v-associated death. Although cases have been identified from 10 states, 2 states (Indiana and Ohio) have reported 245 (80 percent) of the 306 cases. Direct contact with swine has been reported by the vast majority of cases, and influenza A (H3N2) viruses have been identified from swine that are genetically similar to H3N2v viruses from humans. Suspected human-to-human transmission has been identified in a small number of cases, but ongoing community transmission of this virus has not been detected. The median age of patients was 6 years, with 284 (93 percent) aged under 18 years; 52 percent were female (CDC, unpublished data, 2012).

In addition, 3 cases of influenza A (H1N2) variant (H1N2v) virus infection and one case of influenza A (H1N1) variant (H1N1v) virus were detected during this period as a result of enhanced surveillance activities for H3N2v. All 4 patients reported direct exposure to swine in the week before illness onset; one was hospitalized, and all 4 have recovered.

Worldwide
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During 12 May to 22 Sep 2012, typical seasonal patterns of influenza activity occurred in the temperate climate Southern Hemisphere countries. In Australia, influenza activity began increasing in late May 2012 and peaked in mid-July 2012; influenza A (H3N2) virus predominated with smaller numbers of cases of influenza B virus infection reported. In New Zealand, influenza activity began increasing in late June 2012, peaked in early August 2012, and has since been decreasing. Influenza A (H3N2) virus was overwhelmingly predominant, with lower levels of influenza B virus detected. In South Africa, influenza activity began to increase in early June 2012 with increased levels of activity being reported through August 2012. Influenza A (H3N2) viruses have been reported most commonly, but a larger proportion of influenza-positive specimens in South Africa are influenza B viruses than in Australia or New Zealand. In South America, influenza activity peaked earlier in the season and is now decreasing. Influenza A viruses were reported more frequently than influenza B viruses, but the predominant subtype varied by country. Argentina reported a larger proportion of positive specimens as pH1N1 viruses than other countries in the region, but the overall number of influenza positive specimens there was lower than in previous seasons.

Influenza activity also has been reported from countries with tropical influenza seasonality. The overall level of activity compared with previous seasons and the predominant subtype have varied by country. In South America, influenza A viruses have predominated in Brazil, but in Ecuador and Peru, influenza B viruses have been reported most commonly. Southern and Southeast Asia also have seen a mix of predominant influenza types and subtypes with influenza B and pH1N1 viruses co-circulating in several countries, including Bangladesh, India, Sri Lanka, and Thailand. In temperate climate Northern Hemisphere countries, influenza activity remains low compared with levels of activity during the usual influenza season, with small numbers of influenza A (H3N2), pH1N1, and influenza B viruses identified.

Antigenic Characterization of Influenza Virus Isolates
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The WHO Collaborating Center for Surveillance, Epidemiology, and Control of Influenza, located at CDC, receives and analyzes virus isolates from laboratories worldwide. Among the 111 pH1N1 viruses collected from 20 May to 22 Sep 2012 and analyzed (28 from the United States, 57 from South America, one from Oceania, 17 from Asia, and 8 from Africa), 102 (92 percent) were antigenically similar to A/California/7/2009, the influenza A (H1N1) component of the 2012-2013 influenza vaccine for the Northern Hemisphere. Of the 241 influenza A (H3N2) viruses characterized (157 from the United States, 55 from South America, 4 from North America, 4 from Oceania, 20 from Asia, and one from Africa), all were antigenically similar to A/Victoria/361/2011, the recommended influenza A (H3) vaccine component for the 2012-2013 Northern Hemisphere influenza season. Finally, of 271 influenza B isolates from specimens collected during this period and analyzed by CDC, 113 (42 percent) belong to the B/Yamagata lineage (76 from the United States, 17 from Asia, 2 from Oceania, and 18 from South America) and were antigenically similar to B/Wisconsin/1/2010, the recommended influenza B component for the 2012-2013 Northern Hemisphere influenza vaccine. The remaining 158 (58 percent) belonged to the B/Victoria lineage (93 from the United States, 47 from South America, 15 from Asia, and 3 from Africa), nearly all of which (95 percent) were antigenically similar to B/Brisbane/60/2008, the recommended influenza B component in the 2011-2012 Northern Hemisphere influenza vaccine.

Antiviral Resistance Profiles of Influenza Virus Isolates
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The WHO Collaborating Center for Surveillance, Epidemiology, and Control of Influenza at CDC tested 594 isolates from specimens collected during 20 May-22 Sep 2012 for resistance to influenza antiviral medications. Of the 594 isolates tested for resistance to the neuraminidase inhibitor medications oseltamivir and zanamivir, 238 were international isolates (84 were pH1N1; 76 were influenza A (H3N2), and 78 were influenza B viruses), and 356 were U.S. isolates (30 were pH1N1; 158 were influenza A (H3N2), and 168 were influenza B viruses). Only one virus (a pH1N1 virus from the United States) was found to be resistant to oseltamivir but sensitive to zanamivir, and it contained the H275Y mutation in the neuraminidase. High levels of resistance to the adamantanes (amantadine and rimantadine) persist among pH1N1 viruses and influenza A (H3N2) viruses currently circulating globally (3). All 117 H3N2v viruses available for testing were sensitive to oseltamivir and resistant to the adamantanes.

MMWR Editorial Note
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During 20 May to 22 Sep 2012, pH1N1, influenza A (H3N2), and influenza B viruses co-circulated worldwide. In the United States, more seasonal influenza viruses were detected than in the summer months of previous years (excluding the 2009 pandemic), and influenza A (H3N2) viruses were predominant. Although neither the influenza viruses that will predominate nor the severity of influenza-related disease during the 2012-13 season in the United States can be predicted, antigenic characterization of viral isolates from specimens submitted during the summer demonstrated that the majority of influenza A viruses are antigenically similar to the influenza vaccine strains contained in the Northern Hemisphere 2012-13 vaccine.

H3N2v viruses with the matrix (M) gene from the pH1N1 virus were 1st detected in the United States in July 2011 (4). Since the 1st identification of this virus in humans, direct contact with swine has been documented in almost all cases, but limited human-to-human spread also is suspected. Consistent with the age distribution of cases, serologic studies suggest there is little or no cross-reactive antibody to H3N2v in young children, but some cross-reactive antibodies are evident in older children and adults (5). Although community transmission of this virus has not been identified, the potential for this virus to develop the ability to transmit efficiently from person-to-person is of concern. Rapid and intensive investigation of each variant case is necessary to evaluate the spread of disease and the possibility of person-to-person transmission. State and local health departments should consider increased specimen collection among patients with ILI who 1) seek care at an ILINet provider; 2) are part of an ILI outbreak among children in child-care and school settings, because these settings were associated with person-to-person H3N2v virus transmission in 2011; 3) have an unusual or severe presentation of ILI, including a need for hospitalization; or 4) have medically attended ILI or acute respiratory infection, especially children in counties or states where H3N2v cases have occurred (6).

Annual influenza vaccination remains the best method for preventing influenza and its associated complications (7), but the 2012-13 seasonal influenza vaccine does not provide protection against the H3N2v virus. Treatment with influenza antiviral medications is recommended as early as possible for patients with confirmed or suspected influenza (either seasonal influenza or variant influenza infection) who have severe, complicated, or progressive illness; who require hospitalization; or who are at higher risk for influenza-related complications (8).

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ProMED-mail <promed@promedmail.org>

[In summary: Worldwide influenza activity from 20 May to 22 Sep 2012 was elevated in the temperate Southern Hemisphere and tropical regions compared with their levels outside the usual influenza season. In the United States, low levels of seasonal influenza activity were detected, and influenza A (H3N2) viruses were most commonly identified. Antigenic characterization of viral isolates from specimens submitted during the summer demonstrated that the majority of influenza A viruses are antigenically similar to the influenza vaccine strains contained in the current Northern Hemisphere 2012-13 vaccine available for us this season.

More than 300 cases of the influenza A (H3N2) variant virus were detected in 10 states but not elsewhere. The majority of these cases were associated with direct contact with swine. The majority of recent influenza A viruses are well-matched to the influenza vaccine for this season.

Annual influenza vaccination remains the best method for preventing influenza and its associated complications, but the 2012-13 seasonal influenza vaccine does not provide protection against the H3N2v virus. Although community transmission of this H3N2v has not been identified, the potential for this virus to develop the ability to transmit efficiently from person-to-person is of concern. Rapid and intensive investigation of each variant case is necessary to evaluate the spread of disease and the possibility of person-to-person transmission.

Interested readers should consult the original text via the source URL to obtain details of the literature cited. - Mod.CP

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