Influenza in Canada: 2003-2004 Season

Introduction

Surveillance of influenza in Canada is coordinated through the FluWatch program at the Immunization and Respiratory Infections Division, Centre for Infectious Disease Prevention and Control (CIDPC), Public Health Agency of Canada (PHAC) (formerly Population and Public Health Branch, Health Canada). The Primary objectives of FluWatch, now in its eighth year, include the early detection of influenza outbreaks across the country; the provision of timely and up-to-date information on influenza activity in Canada and abroad to professionals as well as the public; the monitoring of circulating strains of influenza virus, including new sub-types; and contributing to the information needed by the World Health Organization (WHO) for vaccine composition for the following season.

This report provides an epidemiologic summary of influenza activity in Canada during the 2003-2004 season. A short summary of the 2002-2003 season is provided in Appendix A.

Methods

The FluWatch program consists of a network of sentinel laboratories, sentinel clinical practices, and provincial and territorial ministries of health. Three main indicators of influenza activity are reported by the network as aggregate data on a weekly basis throughout the season:

1. laboratory-based influenza virus detection* and strain identification** in Canada;

2. influenza-like illness (ILI) consultation rates from sentinel clinical practices across Canada; and

3. regional influenza activity levels, as assigned by provincial and territorial epidemiologists.

A brief summary of the sources of data for influenza surveillance in Canada are provided below.

Respiratory Virus Detections

Laboratories participating in the FluWatch program report the total number of influenza tests performed (by viral culture and direct antigen detection) as well as the total number of tests positive for influenza to CIDPC, on a weekly basis.

On a less timely basis (bi-monthly to monthly), a proportion of the laboratories that report weekly influenza virus detections across Canada also provide additional detailed epidemiologic and laboratory information to CIDPC (case-by-case data). These data represent a subset of the cumulative weekly detections, supplemented with a small proportion of positive detections by seroconversion (i.e., fourfold rise in antibody titre by any method). Methods used in the detection of influenza included viral culture, direct antigen detection, and seroconversion.

Influenza Virus Strain Identification

The National Microbiology Laboratory (NML), PHAC, conducts national surveillance on human influenza virus strains in collaboration with provincial laboratories and other Canadian hospital- and university-based laboratories and provides this information to the FluWatch program. NML virological surveillance detects and describes antigenic changes in the circulating strains of influenza virus. Canadian influenza virus surveillance information and actual representative strains are shared with the WHO's collaborating centres for influenza to contribute to global influenza monitoring and decision-making for vaccine recommendations for the upcoming season.

ILI Consultations Reported by Sentinel Clinical Practices

FluWatch maintains a network of sentinel clinical practices across the country. For 1-clinic day each week, sentinel clinic sites are asked to report the total number of patients seen for any reason (denominator) and the total number of patients meeting a standard case definition for ILI (numerator). Age group information is also collected. In Alberta, however, age group information was collected only on numerator data; age group for denominator data was generated by applying the Canadian population distribution. Sentinel report forms were either returned by fax, or the information was conveyed via e-mail or telephone to CIDPC on a weekly basis for data collation, analysis and dissemination.

Data from sentinel physicians are weighted by the estimated population in the census division being represented each week. This is done in order to produce a summary ILI rate for the Canadian population. Each week the weights are recalculated based on the actual census divisions with data to report. Weighted rates are summed to create a national ILI rate each week.

Regional Influenza Activity Levels Assessed by Provincial and Territorial Epidemiologists

Provincial and territorial epidemiologists assess the weekly influenza activity level in their respective jurisdictions, using a variety of sources of information, including laboratory reports of influenza detection, sentinel physician reports of ILI surveillance, and reports of outbreaks. In addition, school and work-site absenteeism and emergency department and hospital admission data may also be used in assessing the level of influenza activity. Influenza activity levels are reported to CIDPC as no activity reported, sporadic activity, localized activity, or widespread activity***.

Influenza Hospitalizations in Children - Pilot Study

At the beginning of the 2003-2004 influenza season, following reports of influenza deaths in children in the United Kingdom and the United States, a pilot study was initiated with the Immunization Monitoring Program Active (IMPACT) network of pediatric hospitals to determine the feasibility of hospital-based surveillance of influenza in children.

Laboratory-confirmed cases of influenza that required admission to hospital were identified by a trained nurse monitor at each participating center, after which detailed case report forms were completed, based on information from the hospital chart. Case reports were sent to a data centre in Vancouver, British Columbia for review, data entry and analysis.

International

FluWatch also reports on international influenza activity weekly, as assessed from surveillance reports published by other countries (e.g. US Centers for Disease Control and Prevention in Atlanta) and international surveillance systems (e.g. European Influenza Surveillance Scheme [EISS] and the World Health Organization [WHO]).

Dissemination

During the influenza season, FluWatch disseminates weekly reports to health professionals and the public through a variety of mechanisms, including the CIDPC FAXlink, fax, e-mail, and the Public Health Agency of Canada's Viral Respiratory Diseases' Web site at <http://www.phac-aspc.gc.ca/fluwatch/index-eng.php>.

Beginning in the 2002-2003 season, FluWatch reports were disseminated year round, with biweekly reporting of laboratory detections in Canada and summaries of international activity during the off season (June to September). In addition, summaries of influenza, respiratory syncytial virus (RSV), parainfluenza virus and adenovirus laboratory detection data are made available weekly throughout the year through the Respiratory Virus Detections (RVD) Web site <http://www.phac-aspc.gc.ca/bid-bmi/dsd-dsm/rvdi-divr/index-eng.php>.

Summaries of worldwide influenza activity are included periodically in the CIDPC Infectious Diseases News Brief <http://www.phac-aspc.gc.ca/bid-bmi/dsd-dsm/nb-ab/index-eng.php> and periodic updates on influenza surveillance in Canada are published in the Canada Communicable Disease Report <http://www.phac-aspc.gc.ca/publicat/ccdr-rmtc/index-eng.php>.

Results

Respiratory Virus Detections (aggregate data)

Between 24 August, 2003, and 21 August, 2004, a total of 92,998 influenza tests were performed by 33 laboratories across Canada. Approximately 11,435 (12.3%) of these tests were positive for influenza. Of these, 11,294 (98.7%) were influenza A, and 141 (1.23%) were influenza B. Influenza A predominated across the country, the few influenza B identifications were limited to Quebec and Ontario.

Respiratory Virus Detections (case-by-case data)

Twenty laboratories in 10 provinces reported a total of 7,708 detailed records, including epidemiologic and laboratory details, to CIDPC (Table 1).

Table 1. Laboratory-confirmed cases of Influenza reported to the Centre for Infectious Disease Prevention and Control (CIDPC), by laboratory, Canada, 2003-2004

The majority of influenza cases (82.7%) were laboratory confirmed by virus isolation. Less commonly reported methods of laboratory confirmation included direct antigen detection (17.3% of cases) and serologic testing (0.2% of cases). The same three methods of laboratory confirmation were used in previous seasons; however, use of virus isolation has been increasingly reported over the years.

Table 2 shows laboratory-confirmed data by province/territory, and influenza type and subtype for cases reported during the 2003-2004 season. The largest number and proportion of cases were reported by Quebec (31.0%), Ontario (20.5%), Alberta (13.9%) and Saskatchewan (13.9%). The majority of isolations, (99.5%) were type A viruses.

Table 2. Laboratory-confirmed cases of influenza, by province and influenza type and sub-type, Canada, 2003-2004

Figure 1. Laboratory-confirmed cases of influenza by region, type and week of onset, Canada, 2003-2004

During the 2003-2004 season, the age group with the greatest proportion of laboratory-confirmed cases was the youngest one, 0 to 4 years (33%), which is also the narrowest age grouping. The next group with highest cases of influenza in the 2003-2004 season was the 65 years age group (25.4%) (Figure 2).

Figure 2. Proportionate distribution of laboratory-confirmed influenza cases, by age group, Canada, 2003-2004

Influenza Virus Strain Identification

During the period of 1 October, 2003 to 17 August, 2004, the NML characterized 845 influenza virus samples received from provincial and hospital laboratories (Table 3): three (0.36%) influenza A (H1N1) viruses, one (0.12%) influenza A (H1N2), 801(94.8%) influenza A (H3N2), and 40 (4.7%) influenza B viruses. The hemagglutinin proteins of all influenza A (H1N1 and H1N2) viruses were antigenically similar to the A/New Caledonia/20/99 strain. Of the influenza A (H3N2) isolates, 3.1% were similar antigenically to A/Panama/2007/99, and 96.8% were similar to A/Fujian/411/02 strain. Of the 40 influenza B viruses tested, 7 (17.5%) belonged to the Victoria lineage and were antigenically similar to the vaccine strain B/Hong Kong/330/01 and 33 (82.5%) belonged to the Yamagata lineage and were similar to the B/Sichuan/379/99-like virus.

Table 3. Distribution of influenza strains characterized by the Respiratory Virus Section of the National Microbiology Laboratory for the 2003-2004 influenza season, by province and territory

Influenza A (H3N2) virus, in particular the antigenic variant A/Fujian/411/02-like virus, predominated during the season and was identified in all provinces and territories (Figure 3).

Figure 3. Seasonal distribution of laboratory-confirmed influenza infections by influenza type, Canada, 1997-2004

ILI Consultations Reported by Sentinel Clinical Practices

During the 2003-2004 influenza season, sentinels reported an overall ILI rate of 24 per 1,000 patients seen.

ILI reporting rates peaked at week 52 with a rate of 80 per 1,000 patients seen. Between week 40 and 52 rates remained at or below the 1996-2003 mean rates. After week 52, rates remained lower than the mean rate. During week 52, the age group with the highest ILI rate was the 5 to 19 year olds with a rate of 146/1,000, followed by the 0-4 year olds 67/1,000, the 20-64 age group 59/1,000 and the lowest group was the 65 years age group 18/1,000 (Figure 4).

Figure 4. Census division weighted age-standardized ILI rates*, by influenza season and reportweek, Canada, 2003-2004, compared with seasons 1996-1997 to 2002-2003 (average with 95% confidence intervals)

* influenza-like illness rates ([S reported ILI cases + S reported patient visits] x 1,000)

Influenza Activity Level Assessment

Alberta and Saskatchewan were the first provinces to report localized influenza activity in the week ending 4 October, 2003 (week 40). The number of regions reporting localized activity increased gradually over the following weeks, with peak widespread activity occurring at week 2 (week ending 10 January, 2004). Most activity level reporting occurred over a 6-week period, from week 49 to week 2, with 20 or more regions (up to 54.7% of the 52 influenza surveillance regions across Canada) reporting localized or widespread activity each week (Figure 5).

Figure 5. Number of surveillance regions reporting widespread or localized influenza activity, by week and year, 2004, Canada

Influenza Hospitalizations in Children-Pilot Study

Over the 2003-2004 influenza season, 526 children were hospitalized with influenza in nine participating centres. Weekly admissions ranged over the season, with a peak occurring during the last week of December (week 52) (Figure 6). Cases occurred between September and June, with peak admissions occurring in November in Alberta and Saskatchewan and from December to February for the rest of the country. Influenza A was identified in 99% of cases. Fifty-seven percent of children were < 2 years old. Almost half of all admitted children had underlying health conditions. Four children died of influenza-related complications¹.

Figure 6. Weekly admissions due to influenza in children, 2003-2004

Avian Influenza (H7N3), Canada

Avian influenza (H7) of low pathogenicity was first detected on 19 February, 2004 in birds from a commercial chicken breeder farm in British Columbia's Fraser Valley. The farm was immediately quarantined and all birds were depopulated. Subsequently, highly pathogenic avian influenza (HPAI) was detected on the same farm on 8 March, 2004. Infection spread rapidly, and by mid-May, birds on 42 commercial and 11 backyard premises were infected with HPAI. According to the Canadian Food Inspection Agency (CFIA), most of these premises were concentrated in one of three clusters of infection. Disease spread was contained by restriction of movement and a targeted depopulation program that focussed on rapidly isolating, containing and eliminating cases of avian influenza.

Approximately 200 workers were involved in the depopulation and related activities. Of these workers, two individuals became ill following separate and identifiable contacts with a source of virus and were laboratory-confirmed with an avian influenza A/H7N3 infection. Both cases completely resolved their symptoms which included conjunctivitis, nasal discharge and headache².

By 3 June, surveillance of flocks in the Fraser Valley had not detected any new cases of infection. Depopulation activities were officially suspended on 4 June³.

International

Avian Influenza (H7N2 and H5N2), United States

In February, 2004, two low-pathogenic strains of avian influenza (H7N2 and H2N2) were detected in a non-commercial poultry flock in Delaware, and live bird markets in New Jersey. Both the non-commercial poultry premise and the infected live bird market were depopulated.

Routine surveillance detected low-pathogenic avian influenza (H2N2) in one poultry flock in Pennsylvania. Since no clinical signs of illness, increases in mortality or decreases in egg production were observed in the flock, no depopulation was carried out, but the premises were placed under quarantine.

An outbreak of highly pathogenic avian influenza (H5N2) was detected in a single flock in southeast Texas in February 2004 and was subsequently depopulated. Further epidemiologic investigation identified two live bird markets in Houston, Texas, with links to the index premises. As a precaution, all five live bird markets in Houston were depopulated, cleaned and disinfected.

In March, routine testing detected H7N2 (low pathogenicity) avian influenza on one farm in Maryland which was subsequently depopulated. No known human cases of avian influenza have been related to these outbreaks of avian influenza in poultry⁴.

Avian Influenza (H5N1), Asia

On 12 December, 2003, South Korea reported to the World Organization of Animal Health (OIE) that a highly pathogenic avian influenza A/H5 subtype virus had infected birds on a poultry farm. Subsequent to this, the virus was identified as an H5N1 strain and the infection was further identified in birds in several countries, including Cambodia, China, Indonesia, Japan, Laos, South Korea, Thailand and VietNam. On 13 January, 2004, the WHO reported that the infection had passed to humans and that three individuals in VietNam had a confirmed avian influenza A/H5N1 infection. At the end of March 2004, the WHO indicated that there was one probable case and a total 35 individuals were confirmed with an infection in Thailand (12) and VietNam (23); 24 (69%) of these confirmed cases died from their illness. All individuals with a confirmed H5N1 infection were severely ill, and had a history of exposure to sick or dead poultry. The ages for the probable and confirmed infections ranged from 1 to 58 years old, while the mean and median ages were 16.6 and 13 years, respectively. Females consisted of 41.6% of infections and their ages ranged from 1 to 58 years with a median of 20 years while the age range for males whose age was known was 2 to 29 years, with a median of 11 years.

According to the OIE and FAO, a second wave of avian influenza outbreaks began late in June. At the end of August 2004, the outbreaks of avian influenza A/H5N1 were reported to have affected birds in China, Indonesia, Malaysia, Thailand and Vietnam. On 12 August, 2004, the Ministry of Health in Vietnam informed the WHO that three recent human deaths from influenza-like illness in Vietnam were caused by infection with avian influenza, which were confirmed as H5N1 strain infections. These were the first officially reported cases of avian influenza in Vietnam since late February. By the end of October 2004, an additional nine human cases of A/H5 were confirmed, 8 of them fatal. The most recent case was reported on 25 October, 2004 in Thailand. Since January 2004, altogether 44 human cases of A/H5 have been reported from two countries, VietNam and Thailand. Of these cases, 32 have been fatal⁶.

Discussion

Based on a comparison of the national surveillance indicators, this season appeared to be more severe than the past three seasons, but still within the expected range (based on average over a number of years).

Influenza virus began circulating early in Canada this season with Alberta and Saskatchewan being the first provinces to report increased influenza activity in October. By November the rest of the country started reporting laboratory-confirmed influenza with peak activity occurring during the last week of December (week 52). Quebec reported widespread activity for a longer period (week 52 to week 7) than any other province and was also the last to reach the peak of influenza activity at week 7 (week ending 14 February, 2004).

The number of influenza tests and the overall percentage of positive tests was higher than the 2002-2003 season (see appendix for detailed data on the 2002-2003 season). Overall, the number of tests performed have increased considerably since 1996-1997, the first year of the FluWatch program, and earlier^7-13. The variation in the numbers of confirmed cases and their distribution by provinces/territories should be interpreted with caution, as these numbers are likely to reflect differences in population size and distribution, testing and reporting practices and criteria, and availability of diagnostic services. These factors vary among the regions and have changed from year to year.

Similarly, the greatest number of influenza surveillance regions reporting localized or widespread activity occurred during the last week of December.

The weekly proportion of patient visits to approximately 200 sentinel providers nationwide for ILI ranged from 15 to a peak of 79 visits per 1,000 patient visits (week 52, ending 27 December, 2003), which was at or below the weekly average for the preceding seven influenza seasons.

Influenza A predominated across the country this season and accounted for 99.5% of the positive influenza identifications. The predominant strain was the A/Fujian/411/ 2002 (H3N2)-like virus, however earlier in the season A/Panama/2007/99 (H3N2)-like viruses were circulating.

The few influenza B detections occurred in Ontario, Quebec and Nova Scotia. Of the 10 influenza B viruses characterized, 2 belonged to the Victoria lineage and were similar to the vaccine strain B/Hong Kong/330/2001 (recommended influenza B component of the 2003-2004 influenza vaccine), eight were similar to B/Sichuan/379/99 which belongs to the B/Yamagata lineage, and was the recommended influenza B component of the 2001-2002 influenza vaccine. The few influenza B strains appeared in January 2004.

Of the laboratory confirmed influenza infections reported to the Public Health Agency of Canada this season, 45.6% have been reported in children < 15 years of age (31% in children < 4 years of age). The percentage of laboratory-confirmed cases reported for those in the >= 65 year age group has increased to 25% in the 2003-2004 season, which was dominated by influenza A (H3N2), from only 7% in the 2002-2003 season, which was dominated by influenza A (H1N2).

Data from the pediatric hospitalizations pilot study indicated that influenza causes a significant burden in younger children. There were four influenza-related deaths reported through this pilot surveillance. The 2003-2004 season being the pilot year, no previous data were available for comparison. Further surveillance on pediatric hospitalizations due to influenza will be carried out and subsequently comparisons will be made to this year.

From November to December 2003, PHAC received four reports of deaths associated with laboratory-confirmed influenza A infection in children < 15 years of age (range 7 to 14 years). Three additional deaths were reported through the pediatric hospitalizations pilot study, bringing the total to seven influenza-related deaths in children and adolescents over the season.

Globally, influenza A (H3N2) viruses predominated in most countries while influenza B viruses circulated at low levels. Many countries in the Northern hemisphere, including the United States experienced the same predominance of A/Fujian/411/2002 (H3N2)-like viruses. Sporadic activity of influenza B was reported, however no outbreaks were reported. The majority of the recent isolates were from the B/Victoria/2/87 lineage and B/Yamagata/16/88 lineage¹⁴.

The H5N1 avian influenza is unprecedented in its scope, with nine Asian countries affected by poultry outbreaks. Of great concern is the documented transmission to humans and the lethality of this infection in previously young healthy children and adults. Although the virus has not acquired the ability to transmit well from person to person, the WHO and the Global Influenza network have begun a number of preparedness activities, including vaccine development.

The Canadian Pandemic Influenza Plan was published in February 2004 and provides an overall national framework for preparing and responding to an influenza pandemic in Canada. The plan can be accessed via the PHAC website at <http://www.phac-aspc.gc.ca/cpip-pclcpi/index.html>.

References

1. Moore DL, Vaudry W, Scheifele D et al. Canadian children hospitalized for influenza at immunization monitoring program active (IMPACT) Centres, 2003-2004. Abstract presented at the Canadian Immunization Conference, Montreal, Quebec.

2. Tweed SA, Skowronski DM, David ST et al. Human illness from avian influenza H7N3, British Columbia. Emerg Infect Dis 2004; December <http://www.cdc.gov/ncidod/EID/vol10no12/04-0961.htm>.

3. Canadian Food Inspection Agency, Government of Canada. Avian influenza <http://www.inspection.gc.ca/ english/anima/heasan/disemala/avflu/avflue.shtml>.

4. Animal and Plant Health Inspection Service, US Government. Avian influenza in the United States. <http://www.aphis.usda.gov/lpa/issues/ai_us/ai_us. html>.

5. World Organization for Animal Health (OIE) <http://www.oie.int/eng/en_index.htm>.

6. World Health Organization (WHO) <http://www.who.int/ csr/don/archive/disease/influenza/en/>.

7. LCDC. Influenza in Canada - 1999-2000 season. CCDR 2001;27:1-9.

8. LCDC. Influenza in Canada - 1998-1999 season. CCDR 1999;25:185-92.

9. LCDC. Influenza in Canada - 1997-1998 season. CCDR 1998;24:169-76.

10. LCDC. Influenza in Canada - 1996-1997 season. CCDR 1997;23:185-92.

11. LCDC. Influenza in Canada - 1995-1996 Season. CCDR 1996;22:193-99.

12. LCDC. Influenza in Canada - 1994-1995 Season. CCDR 1995;21:205-12.

13. LCDC. Influenza in Canada, 1993-1994 Season. CCDR 1994;20-21:185-91.

14. Weekly Epidemiologic Record 2004;79(10) <http://www.who.int/wer/2004/wer7910/en/>.

Source: S Aziz, MSc, TWS Tam, MD, FRCPC, JF Macey, MA, MSc, Division of Immunization and Respiratory Diseases, CIDPC, Public Health Agency of Canada; Y Li, PhD, Influenza and Respiratory Virus Section, National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg; S Jain, MSc, D Boulos, MSc, H Zheng, B Winchester, MSc, and P Zabchuk, Division of Immunization and Respiratory Diseases, CIDPC, Public Health Agency of Canada.

* Laboratory-based influenza virus detections are reported through the Respiratory Virus Detections system, which continues year-round (August-August).

** Strain identifications are reported by the National Microbiology Laboratory.

*** 1 = No activity reported. 2 = Sporadic: sporadically occurring ILI and confirmed influenza* with NO outbreaks detected within the influenza surveillance region†. 3 = Localized: sporadically occurring ILI and confirmed influenza* together with outbreaks of ILI in schools and worksites or laboratory confirmed influenza in residential institutions occurring in less than 50% of the influenza surveillance region(s)†. 4 = Widespread: sporadically occurring ILI and confirmed influenza* together with outbreaks of ILI in schools and worksites or laboratory confirmed influenza in residential institutions occurring in greater than or equal to 50% of the influenza surveillance region(s)†

* confirmation of influenza within the surveillance region at any time within the prior 4 weeks.

† sub-regions within the province or territory as defined by the provincial/territorial epidemiologist.

Appendix A: Summary of 2002-2003 Influenza Season

The 2002-2003 influenza season in Canada was relatively mild according to national surveillance indicators. Both influenza A and B predominated, with influenza A peaking during the first week of January and influenza B peaking during the last 2 weeks of March.

Respiratory Virus Detections

Overall, the 2002-2003 influenza season was a mixed season of influenza A and B. Influenza A predominated in Quebec and Ontario while influenza B predominated in the prairies, British Colombia and the Atlantic provinces. Between 25 August, 2002 and 23 August, 2003, a total of 60,725 influenza tests were done by 31 laboratories. Approximately 6% (3,517) of tests were positive. Of these 2,054 (58%) were influenza A and 1,463 (42%) were influenza B.

For the 2002-2003 season 2,953 detailed records were reported by 20 laboratories in 10 provinces. The largest proportions of cases were reported from Quebec (28%) Ontario (22%) and Alberta (20%). A higher proportion of cases were influenza A (55%) and 45% were influenza B. Of the 163 influenza A subtypes identified, 5% were HI and 95% were H3N2.

Influenza Virus Strain Identification

The National Microbiology Laboratory (NML) antigenically characterized 564 influenza viruses (table 3): 91 (16%) were influenza A (H3N2) viruses, 345 (61%) were influenza A(H1), in which, 81(23%) were N1, and 264 (77%) were N2. 128 (23%) were influenza B viruses. All 345 influenza A(H1) were antigenically similar to the hemagglutinin of the vaccine strain A/New Caledonia/20/99(H1N1). The neuraminidase of the H1N2 viruses were closely related to the contemporary H3N2 viruses. All of the influenza A (H3N2) isolates were antigenically similar to A/Panama/ 2007/99. Most of the influenza B viruses characterized belonged to the Victoria lineage and were similar antigenically to the vaccine strain B/Hong Kong/330/01.

ILI Reported by Sentinel Physicians

During the 2002-2003 season, sentinel physicians reported 10 to 40 visits for influenza-like illness (ILI) per 1,000 patient visits per week, which was at or below the weekly average for the preceding six influenza seasons.

Influenza Activity Level Assessment

Ontario was the first province to report localized activity in the week 47. Over the next 10 weeks, reporting of localized increased gradually. Widespread activity reporting started later in week 9 in Prince Edward Island. After week 9, widespread activity was reported in Saskatchewan and Nova Scotia during week 11 through 13 and 12 through 17 respectively. The peak in activity level reporting occurred from week 10 to 14, where 20 or more regions reported localized or widespread activity each week.

Globally, the majority of influenza A (H1N1) and A (H1N2) viruses were antigenically closely related to A/New Caledonia/20/99. The neuraminidases of H1N2 viruses were closely related to those of contemporary H3N2 viruses.

Asia (China - Hong Kong): Avian Influenza Infections in Birds and Humans

In January of 2003, highly pathogenic avian influenza A/H5N1 was reported on four chicken farms in Hong Kong. Although not associated with the outbreak in birds, two individuals in Hong Kong, a 33-year-old male and his 9-year-old son, were confirmed with an influenza A/H5N1 infection. Both cases developed their illness after traveling to the Fujian province of China in February. The father developed symptoms on 7 February and later died while his son recovered.

Netherlands: Avian Influenza Human Infections

Widespread outbreaks of a highly pathogenic strain of avian influenza A/H7N7 were reported in poultry farms in the Netherlands over February to May of 2003. The outbreak spread to poultry in Belgium (April 2003) and Germany (May 2003). The WHO reported that the outbreak resulted in 89 confirmed cases of human influenza A/H7N7 infection in the Netherlands, one of which resulted in death. Seventy-nine of these cases exhibited conjunctivitis and 13 of them displayed only mild influenza-like illness symptoms. Three family members of two poultry worker have also fallen ill with a minor respiratory disease, suggesting a possible chain of human-to-human transmission.