Influenza update - 09 September 2011
Update number 142
- Countries in the temperate zone of the northern hemisphere
- Countries in the tropical zone
- Countries in the temperate zone of the southern hemisphere
- From the peer-reviewed literature
- Virological surveillance
• Countries in the temperate regions of the northern hemisphere reported low or undetectable influenza activity. The United States of America (USA) has recently reported four human cases of swine influenza A(H3N2) containing a novel reassortment with an M gene derived from influenza A(H1N1)2009.
• Influenza activity the tropical zone was mostly low with the exception of a few countries of the Americas (Cuba and Honduras), Western Africa (Cameroon and Senegal), and Southern Asia (Bangladesh and Thailand) that reported continued transmission.
• In South America the influenza season has been mild and has peaked with variation in the predominant type and subtype of virus circulating in different countries in the area. Influenza activity may have peaked nationally in Australia, though regional increases are still being reported. New South Wales, Australia has recently reported a cluster of 25 cases with oseltamivir-resistant influenza A(H1N1)2009 virus infection. The cases occurred in a limited geographic area but occurred over a three month period of time. Of note, none of the cases interviewed had previously been exposed to oseltamivir or had other risk factors previously associated with the development of oseltamivir resistance. This represents the largest cluster of oseltamivir resistant viruses to date and the most persistent period of community transmission. Investigations are ongoing to determine the full extent of spread of the virus.
The countries in the northern hemisphere temperate zone are in their inter-seasonal period for influenza. Nearly all of the countries in this zone reported low or no influenza activity. Of interest, the USA Centers for Disease Control and Prevention (CDC) has reported four cases of swine influenza A(H3N2) virus in children in the states of Indiana (1 case) and Pennsylvania (three cases). The virus is similar to one that has been circulating in swine since 1998 and which has been previously identified in eight human cases. The viral genome contains seven of the eight gene segments from the circulating swine H3N2 viruses, including the hemaglutinin and neuraminidase genes, however, it is unique in that it contains one gene segment, the M gene, derived from the pandemic influenza A(H1N1) virus. The swine H3N2 viruses have antigenic cross-reactivity with human H3N2 viruses circulating in the 1990s. The Indiana case did not have direct exposure to pigs but had contact with a care-giver who did have recent swine contact. The three cases in Pennsylvania had all recently visited a fair where swine were present. The virus does not appear to have spread widely in humans; however, investigations are ongoing.
For more information, see the CDC Morbidity and Mortality Weekly Report, September 9, 2011 / 60(35);1213-1215 and the Pennsylvania Department of Health website.
In Central and tropical South America, several countries reported low levels of influenza transmission. In the Dominican Republic, influenza transmission continued to decrease from a peak in July with influenza type B now the predominant influenza virus detected. Influenza virus detections in Cuba have increased steadily over the last 4 weeks, with influenza A(H3N2) accounting for the large majority. Honduras has also reported increasing detections of influenza A(H3N2) during the same period of time associated with and increasing proportion of hospitalizations for severe acute respiratory infection (SARI) and is higher than during the same period of 2010; one SARI related death was reported over the last 2 reporting weeks. Other Central American countries reported no or very low influenza activity. In tropical South America, transmission in Brazil peaked in late June or early July and has returned to low levels. Transmission in Brazil was evenly distributed between influenza A(H1N1)2009 and A(H3N2), with smaller amounts of influenza type B. A similar pattern and time course was noted in Bolivia and Columbia.
Influenza activity in most of tropical Asia is now low. In southern Asia India, Bangladesh, Thailand, and Singapore have recently reported moderate influenza transmission, most of which has been influenza A(H3N2) with very small numbers influenza type B. Transmission in these countries appears to have peaked in mid July, although some low level transmission has continued recently. In South East Asia, Viet Nam and Cambodia have had influenza A(H1N1)2009 transmission mixed with influenza type B. In both countries, transmission appears to be declining since early August. Notably, the severe viral pneumonia surveillance system has detected 27 cases (27% of all tested) that were positive for influenza virus. Of these 27 positive samples, 26 (96%) were pA/H1N1 and 1 (4%) was type B influenza virus.
In sub-Saharan Africa, influenza transmission has continued in the west though detection rates have decreased in Ghana and Togo since peaking in mid July. Transmission in Cameroon has, however, has continued to increase in recent weeks. In all three countries, virus detections have been both influenza A(H1N1)2009 and type B in fairly equal proportions. In eastern Africa, transmission in Kenya has been continuous since the peak in March, though at much lower levels. Virus detections there have been both influenza A(H1N1)2009 and influenza type B.
In South America, the influenza season appears to have peaked and several indicators suggest that the season has been mild in comparison with previous years. In Chile, influenza-like illness (ILI) activity has remained low in comparison to previous years with a peak of 7 consultations per 100,000 inhabitants. Admissions for respiratory infections in children and the number of samples testing positive for influenza have also remain low; although two deaths associated with influenza A(H1N1)2009 were registered over the last two reporting weeks. Influenza A(H1N1)2009 has accounted for the large majority of both ILI and SARI cases in Chile this season. Virus detections and respiratory disease activity in Chile appeared to level off in mid August. ILI, pneumonia, and influenza virus detections in Argentina all peaked 3 to 4 weeks earlier in Argentina than in Chile. All three have been at moderate levels compared to five year national averages. In contrast to Chile, Argentina started the season with a predominance of influenza A(H1N1)2009 but transitioned to a predominance of influenza A(H3N2) by mid season in late July after which very little H1N1 was detected. In Uruguay, respiratory disease activity also appears to have leveled off in late July or early August. The proportions of SARI hospitalizations and SARI ICU admissions were below 5% and 15% respectively and the proportion of SARI deaths decreased below 2%. The large majority of virus detections in Uruguay have been H1N1 (2009) with smaller amounts of H3N2 early in the season.
Influenza transmission in South Africa has remained at low level since peaking in early June.
Australia, New Zealand and South Pacific
The state of New South Wales, Australia has reported an unusual cluster of influenza cases infected with oseltamivir resistant A(H1N1)2009 viruses in the Newcastle region. Twenty-five influenza cases have been identified over a three month period. The viruses all carry the H275Y substitution, which is known to confer high level oseltamivir resistance. In contrast, only two detections of viruses with this genetic marker for oseltamivir resistance have been detected in the country previously this year, one in January and one in March. The first resistant virus was detected in the Newcastle region in May, the most recent in August; 14% of viruses from Newcastle tested during that time have the H275Y substitution. Of 16 cases that have been interviewed, none had previously been treated or exposed to oseltamivir and 15 of the 16 live within a 50 kilometer radius. The epidemiological picture is one of community transmission of the resistant virus in a limited geographic area so far. Of note, all of the resistant viruses are similar antigenically to the H1N1 strain contained in the current trivalent seasonal influenza vaccine, indicating that vaccination would provide protection. The New South Wales Health department is continuing to investigate.
For more information, see the New South Wales Health department website.
Overall, influenza activity appears to have peaked in much of the country, though regional increases are still being reported in some areas. Specifically, influenza notifications have decreased in Queensland, New South Wales, and South Australia but other states continue to report increases. The Influenza Complications Alert Network sentinel hospital system in Victoria, South Australia, Western Australia and the Australia Capital Territory (ACT) reported 88 hospitalizations, including seven ICU admissions, associated with influenza since 1 May 2011. Over half of the hospitalizations and 71% of ICU admissions have been associated with influenza A(H1N1)2009 infection. The mean age of patients hospitalized has been 47.3 years. The Australian Paediatric Surveillance Unit reported 24 hospitalizations associated with severe influenza complications in children from 1 July till 22 August, including nine ICU admissions with the majority also associated with influenza A(H1N1)2009; notably, more than one third of cases hospitalized had chronic underlying conditions. In 2011, 11 influenza associated deaths have been notified nationally to date with a median age of 53 years. Eight of the cases were reported as having an influenza A(H1N1)2009, two with influenza type B and one with an un-subtyped influenza A infection. In NSW, the death registration data up to 5 August 2011 was below the seasonal threshold for this period with 1.8 pneumonia or influenza associated deaths per 100 000 population. The country continues to have some regional variation in the predominant type or subtype of influenza virus being detected. In recent weeks the proportion of influenza type B in South Australia has continued to decline and currently represents a significant proportion (43%) of influenza notifications, with the remainder being mostly influenza A(H1N1)2009. The majority of Australian states and territories now have influenza A(H1N1)2009 more commonly detected, with co-circulation of influenza type B; however, in Tasmania influenza type B accounts for the majority of influenza virus detections and Western Australia is reporting a mix of mostly influenza A(H1N1)2009, A(H3N2) and some influenza type B.
In New Zealand, the rate of national ILI consultations was 55.5 per 100 000 (210 ILI consultations) and remains stable around the seasonal threshold level. Influenza type B virus accounts for the majority of influenza viruses detected in New Zealand. In the Pacific Islands, most countries reported low influenza activity with the exception of Samoa, Tonga, the Solomon Islands and Kiribati. Samoa has experienced an increase in ILI. Tonga, the Solomon Islands and Kiribati reported sustained activity. Fiji reported fluctuating ILI activity, but the level has declined over the past five weeks.
Researchers in China have reported an association between the occurrence of narcolepsy and respiratory disease. In a cross-sectional retrospective ecological study examining the history of narcolepsy onset in 629 patients (mostly children) diagnosed with narcolepsy in Beijing, China between 1998 and 2010, researchers identified a seasonal pattern in the onset, with highest observed incidence in April to July. A three to four fold increase in even this peak incidence was noted in 2010 (per a linear trend line fit to the past time series), mirroring the reported increase in influenza cases from official sources during the 2009/10 winter season. The majority of these 154 narcolepsy cases in 2010 were young children, and only 4% of these cases reported receiving an H1N1 vaccination (using a nonadjuvanted H1N1 monovalent vaccine). Finding, in their study, an association between infection and narcolepsy, but not an association with vaccination, the authors suggest that winter airway infections, including influenza A and/or S.pyogenes are the likely triggers for narcolepsy. The authors felt that the 4-6 month delay between winter airway infection and narcolepsy onset occurrence was consistent with animal studies showing that approximately 80% cell loss is required to exhibit symptoms; winter airway infections could initiate or reactivate an immune response that leads to hypocretin cell loss and narcolepsy in generally susceptible individuals.
Comment: While influenza is considered primarily a disease of the respiratory tract, it is clear that it may on occasion cause disease in other body systems, including the central nervous system. An association between "winter airway infections" and neurological complications was also noted in the years surrounding the 1918 pandemic and neurological complications have been reported in numerous case series from seasonal influenza A(H3N2) epidemics and the 2009/10 influenza A(H1N1)2009 pandemic. Influenza infection has been linked to cases of encephalopathy, seizures, and altered level of consciousness. Neurological manifestations are occasionally the presenting illness with influenza infection and likely occur more often in children and adolescents.
Reference: Han, F., et al. Narcolepsy onset is seasonal and increased following the 2009 H1N1 pandemic in China, 2011, Annals of Neurology. doi: 10.1002/ana.22587(2011).
Source of data
The Global Influenza Programme monitors influenza activity worldwide and publishes an update every two weeks.
The updates are based on available epidemiological and virological data sources, including FluNet (reported by the Global Influenza Surveillance and Response System) and influenza reports from WHO Regional Offices and Member States. Completeness can vary among updates due to availability and quality of data available at the time when the update is developed.