Influenza update - 29 July 2011
Update number 139
- 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
• Influenza activity in the temperate regions of the northern hemisphere remains low or undetectable.
• In the tropical zone, influenza transmission has continued in a few countries of the Americas, in the Dominican Republic, El Salvador, and Colombia; western Africa, primarily reported from Ghana and Cameroon; and parts of Asia in India, Bangladesh, and Singapore.
• Influenza transmission in South Africa has declined to low levels, though virus continues to be detected. Influenza A(H1N1)2009 is the primary type reported. In Australia, influenza-like illness (ILI) consultations and laboratory-confirmed cases continue to increase. ILI activity in New Zealand had crossed national baseline levels previously but are back to the baseline in the most recent report.
Little to no influenza activity has been reported for temperate countries of the northern hemisphere since the influenza season ended.
A few countries in the tropical zone of the Americas have been experiencing significant transmission of influenza. In the Dominican Republic, influenza virus transmission is persisting with co-circulation of influenza A(H1N1)2009 and influenza type B. Transmission of H1N1 (2009) has been noted since late March of this year. In El Salvador, the previously reported circulation of influenza type B is decreasing while respiratory syncytial virus (RSV) is increasing. Circulation of both H1N1 (2009) and H3N2 continues in Colombia but also appears to be decreasing.
In sub-Saharan Africa, Ghana and Cameroon continue to report circulation of influenza type B virus as the predominant type with smaller numbers of H1N1 (2009) and H3N2 noted in Ghana. In Madagascar, virus detections have increased in recent weeks but have shifted from predominance of influenza type B to H1N1 (2009)
Influenza activity remains low in tropical Asia although transmission in some countries has been persisting in the recent weeks. Low levels of influenza A(H3N2) circulation were reported from India, Bangladesh and Singapore. In Singapore, influenza-like illness (ILI) remains low at 2% of polyclinic attendances for acute respiratory illness although H3N2 detections have been increasing over the past 4 to 5 weeks; the proportion of ILI cases tested positive for influenza was 53% in their most recent report. Vietnam continues to report sustained transmission of influenza A(H1N1)2009 and some influenza type B.
Although influenza activity remains low in the South American temperate region, there has been some increase reported in respiratory disease activity recently. In Chile, the number of ILI consultations continues to be low and is similar to the previous week; no deaths from influenza have been reported. However, the number of detections of influenza A(H1N1)2009 viruses, while low, has increased in recent weeks. In Argentina, influenza virus detections, which had increased slightly in late June, are declining in numbers. The percentage of specimens that tested positive for influenza decreased to just below 1.5%. Of the viruses subtyped in Argentina, H1N1 (2009) is the most common type. Notably, the Argentinean province of Mendoza reported a peak in pneumonia cases in early July that was 25% higher than the same time period last year. This coincides with detections of influenza A (untyped) and H1N1 (2009); however, a direct association between the virus and the pneumonia cases has not been reported. Nationally, the numbers of ILI and SARI cases have been decreasing and have not exceeded previously observed levels. In Uruguay, recent increases have been noted in the percent of hospital admissions, intensive care admissions, and deaths with respiratory causes. SARI accounted for 22% of all intensive care admissions in epidemiological week 28 (mid July) compared to less than 5% for seeks in May and early June. Very little virological data are available from Uruguay.
This influenza season has decreased to low levels in South Africa after peaking in early to mid June. Most influenza virus transmission is associated with influenza A(H1N1)2009 while influenza A(H3N2) and type B are detected in much smaller numbers. Influenza type B made up a somewhat larger portion of SARI cases than ILI cases (17% vs. 4% respectively). A new but still preliminary analysis of the influenza cases is available from the National Institute of Communicable Diseases (NICD) on their website. The NICD reports that of 164 SARI cases for which the outcome of their illness is known, five (3%) have died - a lower proportion than during the 2010 season (9%). The age distribution of SARI cases in this season has been similar to the 2010 season with a high proportion of cases occurring in children under the age of 5 years (38% of SARI cases in 2011, 37% in 2010) and adults between the ages of 25 and 45 years (31% in 2011, 35% in 2010). Notably, 47% of 123 cases for which testing was available were positive for human immunodeficiency virus (compared to 57% in 2011). Other risk factors reported include asthma (6%), prematurity (2%), chronic obstructive lunch disease (2%), and heart disease (2%).
Australia, New Zealand and South Pacific
In Australia, notifications of ILI consultations continue to rise from both sentinel general practitioner surveillance sites and emergency departments, particularly from South Australia, Queensland and New South Wales. Queensland reported the largest number of laboratory-confirmed notifications, with 1,555 cases of influenza, followed by New South Wales and South Australia. Influenza A(H1N1)2009 accounted for the majority of virus detections nationally with most of the cases located in Queensland and New South Wales. However, in South Australia influenza type B is more common and the state continues to account for 80% of influenza type B notifications nationally. Low-level transmission of influenza A(H3N2) has also been noted. The numbers of confirmed cases of influenza reported through the National Notifiable Diseases Surveillance System as of 8 July (7,488 cases) remain high compared to the same period in 2010 (1,294 cases). In New Zealand, the rate of national ILI consultations is at baseline level of 49.9 per 100,000 population this week having decreased from 58 per 100,000 population in the previous week. At this time, all 20 district health boards are reporting ILI activity. The majority of the specimens tested positive for influenza was identified as influenza type B, lower number of cases of influenza A(H3N2), H1N1 (2009) and A(not subtyped) were also present. In New Zealand, the rate of national ILI consultations has not crossed the baseline levels although some of the districts were well above the national average. For this week, influenza B virus was the predominant strain followed by influenza A(H3N2) virus.
Investigators at the Massachusetts General Hospital and Harvard Medical School recently reported the results of a study of the serological response of patients with inflammatory bowel disease to a non-adjuvant influenza A(H1N1)2009 monovalent vaccine. The prospective, open-label study measured immunological response in 108 patients with inflammatory bowel disease using hemaglutinin inhibition titers before and after vaccination. Fifty percent of subjects were found to have antibody titers after immunization of a level considered to be protective (titer≥40) after one dose of vaccine containing 15 mg of influenza A/California/07/2009 (H1N1) -like virus haemagglutinin. Subjects who were immunosuppressed as a result of combination drug therapy for their disease were significantly less likely to have protective levels of antibodies than those who were not on immunosuppressive therapy (36% vs. 64% respectively, p=0.02). Similarly, subjects with intermediate levels of T lymphocyte functional activity were less likely to develop protective levels of antibody after vaccination than those with high levels of T lymphocyte functional activity (28% vs. 61% respectively, p=0.02). This study, which received some funding from Sanofi Pasteur (an influenza vaccine manufacturer), illustrates the sometimes poor response to influenza vaccination in persons at highest risk for complications from influenza infection. It re-emphasizes the need for individuals at high risk of severe influenza-related disease to be vaccinated every year before influenza season to increase their likelihood of protection. Individuals at high risk should also continue to practice other means of influenza avoidance such as appropriate hand hygiene and be considered for early empiric treatment even if they have been vaccinated. (Ref: Serological response to the 2009 H1N1 influenza vaccination in patients with inflammatory bowel disease. Cullen G, Bader C, Korzenik JR, et al. Gut (2011). doi:10.1136/gutjnl-2011-300256 available online at: http://gut.bmj.com/content/early/2011/07/13/gutjnl-2011-300256.short?q=w_gut_ahead_tab)
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 Network) 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.