Wind of Change

Editor’s Note: This article will be updated frequently, so check back often for new information. On October 15, updates were made to weekly US influenza data (including college data) and reports of bacterial coinfections. Influenza hospitalization data were added as well.

Novel Influenza A (H1N1) Timeline

February 24, 2009	Patient zero is said to be a 6-month-old girl from northern Mexico, according to Celia Alpuche of the Institute of Epidemiological Diagnosis and Reference in Mexico City. (Cohen J. Swine flu outbreak, day by day. ScienceInsider. July 17, 2009. Available at: http://blogs.sciencemag.org/scienceinsider/special/swine-flu-timeline.html Accessed September 16, 2009.)
March 3, 2009	Initial recognition of case in Mexico City with multiple cases reported on March 18.
April 6, 2009	Outbreak in La Gloria, Mexico, with attack rate of 60%.
April 15, 2009	First virologically defined cases and first recognized US case: 10-year-old boy in California with positive test for influenza H1 antigen but negative for seasonal H1 and H3.
April 26, 2009	United States declares public health emergency.
April 29, 2009	Mexican Ministry of Health reports 1-month total of 2155 patients with severe pneumonia and 100 deaths.
May 9, 2009	Global epidemic recognized with caseloads that matched international air-traffic patterns from Mexico City. (Khan K, Arino J, Hu W, Raposo P, et al. Spread of a novel influenza A (H1N1) virus via global airline transportation. N Engl J Med. 2009;361:212-214. Available at: http://content.nejm.org/cgi/content/full/361/2/212 Accessed September 16, 2009.)
June 11, 2009	WHO (Dr. Margaret Chan, Director General) declares phase 6 pandemic and calls 2009 H1N1 “unstoppable”; also notes that most patients in the world with 2009 H1N1 are younger than 25 years of age and that one third of serious cases are in previously healthy young people.
July 1, 2009	US cases appear in all states; estimated total is more than 1 million infected; 87% of deaths in persons 5-59 years of age.
July 17, 2009	WHO reports 94,512 virologically confirmed cases and 429 deaths, but considers this the “tip of the iceberg.” A decision is made to stop counting cases.(World Health Organization. Chan M. World now at the start of 2009 influenza pandemic. June 11, 2009. Available at: http://www.who.int/mediacentre/news/statements/2009/ h1n1_pandemic_phase6_20090611/en/index.html Accessed September 16, 2009.)
July 20, 2009	Chile reports 2009 H1N1 in turkeys, increasing sources of the virus and introducing the possibility of mixing with avian genes.
August 25, 2009	President’s Council of Advisors anticipates that 2009 H1N1 may infect half of the US population, require 1.8 million hospitalizations, and result in 30,000-90,000 deaths. (President’s Council of Advisors on Science and Technology. U.S. Preparations for 2009-H1N1 Influenza. August 7, 2009. Available at: http://www.whitehouse.gov/assets/documents/PCAST_H1N1_Report.pdf Accessed September 16, 2009.)

Epidemiology and Impact

Updated Influenza Data for United States, Based on CDC Surveillance Data

(CDC, Influenza Division. FluView. Available at: http://www.cdc.gov/flu/weekly/ Accessed September 16, 2009.)

• The week of September 20-26, 2009 showed that outpatient visits for influenza-like illness (ILI) were increased in 9 of 10 Health and Human Services surveillance regions (the exception was region 1, which includes Connecticut, Maine, New Hampshire, Rhode Island, Vermont, and Massachusetts) and that 22.8% of tested specimens were positive for influenza. Of 1129 influenza strains that were subtyped, 1116 (98.8%) were 2009 influenza A (H1N1) viruses, 7 were type B, and 3 were seasonal H3N1.
• Testing of 562 2009 H1N1 strains showed that all were related to the A/California/07/2009 reference virus used in the vaccine.
• Sensitivity tests done on 1865 2009 H1N1 isolates showed 9 (0.5%) to be resistant to oseltamivir; review of these cases showed that 8 patients had documented prior exposure to oseltamivir.
• During the week of September 20-26, pneumonia and influenza accounted for 6.1% of US deaths. This is below the epidemic threshold of 6.4%.

Declining flu activity in colleges. For the week of September 26 to October 2 there were 6326 reported cases of ILI, down 6% from the previous week. Among these cases there were 9 hospitalizations and no deaths. These data are from a survey conducted by the American College Health Association of 273 US colleges and universities, representing 20% of US college students. On the basis of these data, the national estimate for ILI so far this season is 183,000 cases among 18 million college students. (American College Health Association. ACHA Pandemic Influenza Surveillance. Influenza-Like Illnesses in Colleges and Universities. Available at: http://www.acha.org/ILI_surveillance.cfm Accessed October 12, 2009.)

Businesses. A national survey of 1057 randomly selected businesses in 6 categories (small, medium, large; critical or noncritical) was conducted by the Department of Homeland Security and the Harvard School of Public Health The study was funded by the CDC and took place between July 16 and August 12, 2009. Key findings from the survey of businesses (Harvard Opinion Research Program, Harvard School of Public Health. Business Preparedness: Novel Influenza A (H1N1). July 16-August 12, 2009. Available at: http://www.hsph.harvard.edu/news/press-releases/2009-releases/businesses-problems-maintaining-operations-significant-h1n1-flu-outbreak.html Accessed September 16, 2009.):

• 74% provide paid sick leave; 34% offer leave to care for others; 21% provide sick leave to care for children;
• 67% would note operational problems if 50% of workforce was off more than 2 weeks;
• Paid sick leave is offered by 74% and 35% allow paid sick leave to care for family members;
• A doctor’s note is required for sick leave by 43%, and 69% that offer sick leave require a doctor’s note to return after a contagious illness (relevance is concern about physician access in a pandemic);
• Strategies to decrease person-person contact (like staggered shifts) could be implemented by 50% for 1-2 weeks.

Click here for information about business planning for influenza.

Nursing homes. No outbreaks of the 2009 H1N1 virus have been reported to the CDC. This is attributed to the advanced ages of most persons in chronic care facilities, which is a reduced risk for this virus.

Hospitals. Many anticipate a surge of H1N1 influenza cases in the coming influenza season based on the experience in the Southern hemisphere. The President’s Advisors estimate that there will be a 30%-50% attack rate this winter with 1.8 million hospitalizations, which will pose extreme challenges for hospitals. A 2006 Institute of Medicine report indicated that emergency medicine nationwide was “at the breaking point” in both finances and capacity. (Committee on the Future of Emergency Care in the United States Health System, Institute of Medicine. Emergency Medical Services: At the Crossroads. Washington, DC: National Academies Press; 2007.)

An analysis by the Center for Biosecurity at the University of Pittsburgh Medical Center estimated that a severe pandemic would require 4.6-fold more ICU beds and 2-fold more hospital beds. (Bartlett JG, Borio L. Healthcare epidemiology: the current status of planning for pandemic influenza and implications for health care planning in the United States. Clin Infect Dis. 2008;46:919-925.)

These concerns are compounded by the lack of a vaccine for the 2009 H1N1 virus before mid-October and the fact that there may be only enough vaccine for 25% of the target population (assuming that a single dose is required).

New York City. Thomas Farley, MD, MPH, New York City Health Commissioner, said, “We’re seeing essentially no (flu) disease transmitted in the City. We had 750,000 to 1 million sick people last spring. We were the hardest hit city then, so we have a lot of immune people now.” (Hartocollis A, McNeill DG Jr . Areas hit hard by flu in spring see little now. New York Times. October 8, 2009;sect A1.)

Social conventions in France. French companies and schools are discouraging the common greeting of a cheek kiss or hug. Others are also discouraging the handshake and the “high five.” (Schipoliansky C, Cox L. Swine flu cuts the kiss in Europe. ABC News, September 9, 2009. Available at: http://abcnews.go.com/Health/SwineFluNews/swine-flu-cuts-kiss-europe/story?id=8520227 Accessed September 16, 2009.)

Clinical Features of H1N1 Influenza

Typical Signs and Symptoms

The incubation period for H1N1 influenza is 1-4 days, possibly as long as 7 days. The clinical features of influenza are well known and include:

• Sudden onset of fever (usually high);
• Headache;
• Extreme tiredness;
• Dry cough;
• Sore throat;
• Runny nose; and
• Muscle aches and stomach symptoms — more common in children.

(CDC. Interim guidance for clinicians on identifying and caring for patients with swine-origin influenza A (H1N1) virus infection. June 2009. Available at: http://www.cdc.gov/h1n1flu/identifyingpatients.htm Accessed September 16, 2009.)

The symptoms of pandemic H1N1 influenza of 2009 are essentially the same as the seasonal flu, although some have noted an increased frequency of gastrointestinal symptoms, including vomiting and diarrhea, and others have noted the absence of fever in a significant number with virologically proven cases.

The CDC defines cases as influenza-like illness (ILI) if there is fever of ≥100° F (37.8° C) plus cough and/or sore throat in the absence of a known cause other than influenza. Another category is acute respiratory illness (ARI), defined by the presence of 2 of the following 4 symptoms: fever, cough, sore throat, or rhinorrhea. In the outbreak of pandemic influenza in New York City, 95% of virologically proven cases satisfied the ILI definition. (CDC. Swine-origin influenza A (H1N1) virus infections in a school — New York City, April 2009. MMWR Morb Mortal Wkly Rep Dispatch. 2009;58:1-3. Available at: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm58d0430a1.htm Accessed September 25, 2009.)

Patients with 2009 influenza A H1N1 infections have higher rates of gastrointestinal symptoms and lack of fever compared with those who have seasonal flu. Most patients have mild symptoms, but a small subset of previously healthy young adults have severe pulmonary disease that progresses to acute respiratory distress syndrome (ARDS); this may occur with or without underlying conditions.

Symptoms in virologically confirmed cases. During an outbreak of H1N1 in a New York City high school, a sample of New York City school students (median age, 15 years) with virologically confirmed cases were interviewed about their symptoms by telephone. They reported:

• Cough (98%);
• Subjective fever (96%);
• Fatigue (89%);
• Headache (82%);
• Sore throat (82%);
• Abdominal pain (50%);
• Diarrhea (48%);
• Dyspnea (48%); and
• Joint pain (46%).

The measured mean peak fever in this group was 102.2° F. (CDC. Swine-origin influenza A (H1N1) virus infections in a school — New York City, April 2009. MMWR Morb Mortal Wkly Rep Dispatch. 2009;58:1-3. Available at: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm58d0430a1.htm Accessed September 25, 2009.)

Case Definitions for H1N1 Influenza

(CDC. Interim guidance for clinicians on identifying and caring for patients with swine-origin influenza A (H1N1) virus infection. June 2009. Available at: http://www.cdc.gov/h1n1flu/identifyingpatients.htm Accessed September 16, 2009.)

• Confirmed case: Patient with ILI plus laboratory evidence confirmed by real-time RT-PCR or viral culture;
• Probable case: ILI plus laboratory test positive for influenza A and negative for human H1 and H3 by RT-PCR; and
• Optional: ILI without negative H1N1 test and (1) previously healthy person > 65 years hospitalized for ILI; (2) epidemiologic link to confirmed or probable case in past 7 days; or (3) ILI plus travel to a state or country with confirmed or probable cases.

Complications of H1N1 Influenza

• Exacerbation of underlying chronic disease;
• Complications related to the upper airways, including sinusitis or otitis;
• Pulmonary complications, including bronchitis, asthma (sometimes with status asthmaticus), and acute exacerbations of chronic bronchitis; and
• Miscellaneous conditions, including cardiac (myocarditis and pericarditis), myositis, rhabdomyolysis, central nervous system complications (encephalopathy, encephalitis, seizures), toxic shock syndrome, and secondary bacterial pneumonia.

Bacterial coinfections. CDC investigators reviewed clinical records and pathology reports from 77 lethal cases of pandemic H1N1 infection. (CDC. Bacterial coinfections in lung tissue specimens from fatal cases of 2009 pandemic influenza A (H1N1) – US, May – August 2009. MMWR Morb Mortal Wkly Rep. 2009;58: early release) The tissue specimens were examined by tissue Gram stain, Warthin-Starry silver stain, various microbe-specific immunohistochemical assays, and PCR that targeted the 16S ribosomal DNA in tissue blocks. Bacteria were detected in 22 of 77 cases (29%). Major pathogens were Streptococcus pneumoniae (10), Staphylococcus aureus (7), Streptococcus pyogenes (6), Streptococcus mitis (2), and Haemophilus influenzae (1); 4 cases had more than 1 pathogen. The study authors emphasize the importance of bacterial superinfection in patients with influenza. During the 1918-19 pandemic, most deaths were associated with bacterial superinfection. (Morens DS, Taubenberger JK, Fauci AS. Prominent role of bacterial pneumonia as a cause of death in pandemic influenza: implications for pandemic influenza preparedness J Infect Dis. 2008;198:962-970.)

Severe complications of H1N1 Influenza. In June 2009, the University of Michigan reported severe pulmonary complications of 2009 H1N1 influenza infection in 10 patients with a median age of 49 years. All 10 patients were referred for severe hypoxemia, ARDS, and inability to oxygenate with conventional ventilation methods. All had severe multilobar pneumonia on x-ray, none had evidence of bacterial pneumonia, and 4 had CT scan-confirmed pulmonary embolism. Lab findings included leukocytosis in 5 (median WBC 9500/mm³), elevated AST levels (41-109 IU/L) in all 10, and elevated CPK levels (51-6572 IU/L) in 6; none had evidence of disseminated intravascular coagulation. The major risk factor was obesity in 9 and morbid obesity (BMI > 40) in 7. All 10 required advanced mechanical ventilation with high-frequency oscillatory or bilevel ventilation with mean airway pressures of 32-55 cm H₂O. Two required veno-venous extracorporeal membrane oxygenation (ECMO) support and 6 required dialysis. At the time of the report, 3 had died, 1 was still on ECMO, 1 was still on mechanical ventilation, and 5 had been transferred back to referring institutions. (CDC. Intensive care patients with severe novel influenza A (H1N1) virus infection — Michigan, June, 2009. MMWR Morb Mortal Wkly Rep. 2009;58:749-752.)

Neurologic complications. Neurologic complications were reported in 4 children ages 7-17 years with 2009 H1N1 influenza A. Findings included seizures in 2 children, encephalitis in 2, and ataxia in 1. All recovered without neurologic sequelae. The editorial comment in this report noted that the neurologic disease in these 4 patients was less severe than what has been described in previous reports of seasonal flu. (CDC. Neurological complications associated with novel influenza A (H1N1) infection in children — Dallas, Texas, May 2009. MMWR Morb Mortal Wkly Rep. 2009;58:773-778.; Maricich SM, Neuf JL, Lotze TE, et al. Neurologic complications association with influenza A in children during the 2003-2004 influenza season in Houston, Texas. Pediatrics. 2004;114:e626-e633.; Morishima T, Togashi T, Yokota S, et al. Encephalitis and encephalopathy associated with an influenza epidemic in Japan. Clin Infect Dis. 2002;35:512-517.)

Related Risk for Infection, Hospitalization, and Lethal Outcome

Age-related risk. These data are shown in Table 1.

Table 1. Rates for H1N1 for May-July 2009 by Age

Age	Cases/100,000	Hospitalization/100,000	Death %
0-4 yrs	23	4.5	7 (2%)a
5-24 yrs	27	2.1	48 (16%)
25-49 yrs	7	1.1	124 (41%)
50-64 yrs	4	1.2	71 (24%)
> 65 yrs	1.3	1.7	26 (2%)

^a % of total deaths. Age data not available for 15%.
Rate expressed /100,000 population

US age data

(Novel Swine-Origin Influenza A (H1N1) Virus Investigation Team; Dawood FS, Jain S, Finelli L, et al. Emergence of a novel swine-origin influenza A (H1N1) virus in humans. N Engl J Med. 2009;360:2605-2615.)

• Median age of confirmed cases: 12 years
• Median age of hospitalized cases: 20 years
• Median age of lethal cases: 37 years

A comparison of the H1N1 outcome and seasonal flu outcome in elderly individuals is shown in Table 2.

Table 2. Age-Related Outcome With 2009 H1NI Influenza

Compared With Seasonal Influenza in the United States*

	Hospitalized	Deaths
Age > 65 yrs Seasonal flu 2009 H1N1	60% 5%	90% 8%

*CDC. Use of influenza A (H1N1) 2009 monovalent vaccine — recommendations of the Advisory Committee on Immunization Practices (ACIP), 2009. MMWR Morb Mortal Wkly Rep. 2009;58(RR-10):1.
CDC. Update: Swine-origin influenza A (H1N1) virus — United States and other countries. MMWR Wkly. 2009;58:421.

The unusual age distribution of 2009 H1N1 virus infection is attributed to studies showing that persons who were exposed to the 1918 influenza virus have antibody to 2009 H1N1 strains. Related H1N1 influenza strains circulated until 1957, suggesting that people born before this time were likely to be exposed to common antigens. H1N1 viruses re-emerged in 1977 and were antigenically related to viruses circulating in the 1950s, but there is not good evidence of protection from the 2009 H1N1 virus. (Itoh Y, Shinya K, Kiso M. In vitro and in vivo characterization of new swine-origin H1N1 influenza viruses. Nature. 2009;460:1021-1025.)

Risks for serious disease requiring hospitalization or causing death

(CDC. Hospitalized patients with novel influenza A (H1N1) virus infection — California, April-May. MMWR Morb Mortal Wkly Rep. 2009;58:536-541; CDC. Intensive care patients with severe novel influenza A (H1N1) virus infection — Michigan, June 2009. MMWR Morb Mortal Wkly Rep. 2009;58:749-752.)

• Pregnancy: A review of 34 confirmed cases of 2009 H1N1 influenza in pregnant women, reported to the CDC from 13 states, showed that 11 women were hospitalized and 6 died. All 6 deaths were in previously healthy women who developed viral pneumonia and ARDS requiring mechanical ventilation. None of the 5 infants born to these women had evidence of influenza. (Jamieson DJ, Honein MA, Rasmussen SA, et al. H1N1 2009 influenza virus infection during pregnancy in the USA. Lancet. 2009;374:451-458.)
• Other previously defined risks (chronic underlying disease or immunosuppressed) in 117/179 (65%) of hospitalized patients;
• Obesity: 30%-35% of hospitalized patients are obese (BMI ≥ 30) or morbidly obese (BMI > 40). Note that 25% of adults in the United States are obese by this definition and that most of the obese patients hospitalized with H1N1 had other predisposing illnesses. Nevertheless, a rodent model showed excessive mortality in a group of mice fed with a high-fat diet. (Smith AG, Sheridan PA, Tseng RJ, Sheridan JF, Beck MA. Selective impairment in dendritic cell function and altered antigen-specific CD8+ T-cell responses in diet-induced obese mice infected with influenza virus. Immunology. 2009;126:268-279.)

Patients hospitalized with 2009 H1N1 influenza in the United States. The CDC reviewed the medical records from 272 of the 1082 patients hospitalized with influenza as reported to the CDC for the period May 1, 2009 to June 9, 2009. (Jain S, Kamimoto L, Bramley AM, et al. Hospitalized patients with 2009 H1N1 influenza in the United States, April-June, 2009. N Engl J Med. 2009;Oct 8. [Epub ahead of print].) Important observations from this review:

• Age distribution: median age: 21 years; 14 patients were older than 65 (5%);
• Symptoms: vomiting or diarrhea: 39%;
• Associated conditions: any: 198 (73%); asthma: 76 (28%); immunosuppression: 40 (15%); pregnancy: 18 (7%); morbid obesity in adults 26/100 (26%);
• Lab: x-ray showing pneumonia: 100/249 (40%) including 60/100 with bilateral infiltrates; anemia: 87/238 (37%); leukopenia: 50/246 (20%); bacteremia: 3/272 (1%);
• ICU admission: 67 (25%);
• Mortality: 19 (7%) — all were ICU patients given mechanical ventilation; median age was 26 years; median time from onset to death was 15 days; underlying disease present in 13/19 (68%);
• Antimicrobials: antiviral agents were given to 201/268 (75%) starting at a median of 3 days after onset of illness; antibiotics were given to 79%;
• The report notes that oseltamivir or zanamivir is recommended for patients hospitalized with influenza and for those at high risk for complications, even if started later than 48 hours after onset of symptoms. (McGeer A, Green KA, Plevneshi A, et al. Antiviral therapy and outcomes of influenza requiring hospitalization in Ontario, Canada. Clin Infect Dis. 2007;45:1568-1575.)

Surveillance of patients hospitalized with H1N1 influenza

• Most adults have associated risks, especially asthma, chronic lung or heart disease, or immunosuppression;
• Most children have associated risks such as asthma, chronic lung disease, neurologic disease, or sickle cell disease; and
• 6% were pregnant women

(CDC Online Newsroom. Weekly 2009 H1N1 Flu Media Briefing. October 13, 2009. Available at: http://www.cdc.gov/media/transcripts/2009/t091013.htm Accessed October 14, 2009.)

Individuals should seek emergency medical care if they have dyspnea, chest pain or pressure, confusion or seizures, persistent vomiting, or bluish lips. (CDC. H1N1 flu (swine flu): general information, 2009. Available at: http://www.cdc.gov/h1n1flu/general_info.htm Accessed September 16, 2009.)

Epidemiology of H1N1 Influenza

Virus. 2009 H1N1 influenza virus is a quadruple reassortment with gene products from pigs (Europe and Asia origin), avian influenza, and human influenza strains. This virus is antigenically unrelated to H1N1 influenza viruses in circulation since 1957. (Garten RJ, Davis CT, Russell CA, et al. Antigenic and genetic characteristics of swine-origin 2009 A(H1N1) influenza viruses circulating in humans. Science. 2009;325:197-201.; Zimmer SM, Burke DS. Historical perspective — emergence of influenza A (H1N1) viruses. N Engl J Med. 2009;361:279-285.)

As of September 1, 2009, the H1N1 viruses are similar, showing minimal mutation by sequential analysis and by geographic distribution. (CDC. Pneumonia hospitalizations among young children before and after introduction of pneumococcal conjugate vaccine — United States, 1997-2006. MMWR. Morb Mortal Wkly Rep. 2009;58:1-4.)

Laboratory studies show that in the rodent model, compared with seasonal H1N1 strains, the 2009 H1N1 virus replicates in lungs more efficiently, causes different proinflammatory cytokine responses, and results in more lung damage and more death. (Itoh Y, Shinya K, Kiso M. In vitro and in vivo characterization of new swine-origin H1N1 influenza viruses. Nature. 2009;460:1021-1025.)

Transmission rates

• Reproduction ratio (R_O) = 1.4
• Secondary attack rates in households are 8%-18%; the rate is 8%-12% for ILI and 18%-19% for ARI.

Case fatality rate

• Case fatality is reported to be 0.4% (compared with 0.3% in Europe and 2.4% for the 1918-19 influenza pandemic).
• A New York City telephone survey found ILI in 250,000 of 8.3 million people; case-fatality rate was 0.0008%. (New York City Department of Health and Mental Hygiene. Prevalence of flu-like illness in New York City: May 2009. Available at: http://www.nyc.gov/html/doh/downloads/pdf/cd/h1n1_citywide_survey.pdf Accessed September 16, 2009.)
• Data based on confirmed cases are flawed by selected use of testing that favors seriously ill patients. (Garske T, Legrand J, Donnelly CA, et al. Assessing the severity of the novel influenza A/H1N1 pandemic. BMJ. 2009;339:b2840.)

Treatment with ECMO. A study was designed to determine the safety, efficacy, and cost-effectiveness of ECMO compared with conventional ventilation in the treatment of adults with severe acute respiratory failure. There were 120 adults with potentially reversible respiratory failure and Murray score > 3.0 or pH > 7.2. The 6-month survival was 57/90 (63%) for patients allocated to consideration of treatment by ECMO vs 41/87 (47%) for patients allocated to conventional treatment (P = .03). (Peek GJ, Mugford M, Tiruvoipati R, et al. Efficacy and economic assessment of conventional ventilatory support versus extracorporeal membrane oxygenation for severe adult respiratory failure (CESAR): a multicentre randomised controlled trial. Lancet. 2009;Sep 15 [Epub ahead of print].)

Projected cases and impact in the United States

• On August 25, 2009, the President’s Council of Advisors projected that H1N1 may infect up to half of the US population, with hospitalization of 1.8 million and lethal outcome in 30,000-90,000.
• Mortality: Media emphasized the 90,000 figure; Thomas R. Frieden, MD, MPH, Director of the CDC, emphasized the 30,000 figure.
• Impact: President’s Council of Advisors estimates that 50% of 60-120 million will seek medical care, and 300,000 will be hospitalized in ICUs, possibly occupying all ICU beds in most hospitals.

CDC Report on US Influenza A (H1N1) Infections

The CDC has 1600 people dedicated to the influenza effort, according to CDC Director Frieden. The CDC currently estimates that there are 48,000 influenza A (H1N1) infections in the United States and more than 600 deaths. The initial vaccine supply of 2.2 million doses of the nasal spray, the live attenuated virus vaccine, has started to arrive. The CDC is emphasizing the safety of the vaccine to counter the campaign that vaccines are harmful. (McHugh R, Fortuna R, McCarthy K. Swine flu ground zero: a rare look into CDC. ABC News. October 13, 2009. Available at: http://abcnews.go.com/m/screen?id=8778094&pid=4380645 Accessed October 13, 2009.)

Experience in New Zealand With H1N1 Influenza

This experience is valuable because New Zealand has good surveillance systems and is in the Southern hemisphere, so the country’s winter flu season with simultaneous seasonal flu and pandemic H1N1 flu is largely over. (CDC. Surveillance for the 2009 pandemic influenza A (H1N1) virus and seasonal influenza viruses — New Zealand, 2009. MMWR Morb Mortal Wkly Rep. 2009;58:918-921.)

Sentinel GP surveillance system. Defines ILI activity based on reports of volunteer general practitioners. Rates of 50-249/100,000 population/week are considered average for normal seasonal flu activity. Rates > 400/100,000 define epidemic levels. The highest rate was 287 consultations/100,000 population for July 13-19, 2009; this is 3 times the peak rate of 95/100,00 in 2008.

Virology. Analysis of 527 influenza virus isolates in the sentinel surveillance labs (527 strains) and the nonsentinel labs (3931 strains) showed that 2009 H1N1 influenza A accounted for about 65% of identified strains.

Patients. The ILI rates (expressed per 100,000 population) in rank order: children 1-4 years (154); infants < 1 year (110); 15-17 years (97); 20-34 years (96); 35-49 years (66); 50-64 years (57); and ≥ 65 years (23).

Australia

Like New Zealand, Australia represents a model of what may occur in the northern hemisphere because it represents a southern hemisphere country with good surveillance and recent simultaneous epidemics of 2009 H1N1 and seasonal flu. Highlights of a recent influenza report from this country:

• Case counts: Confirmed cases: 35,936 (underreported); hospitalized: 4649; deaths: 169 (3.6% of hospitalized patients, Table 3)

Table 3. Influenza Outcomes in Australia

Severe Cases	Hospitalized	ICUb	Death
Median age (yrs) Comorbidity Pregnancy	31 64%a 4%a	43 63% 13%	53 — 2.5%

^a % of hospitalized patients
^b ICU patients: 75% required mechanical ventilation and 14% required ECMO.(Dwyer DE. Mini Lecture. Pandemic influenza (H1N1)09 activity in Australia – implications for the northern hemisphere. Program and abstracts of the 49th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC); September 12-15, 2009; San Francisco, California. Abstract V-1269a.)

• Issue of transplantation of non-lung organs: single case with no transfer of infection. Viremia is rare compared with influenza due to H5N1, and autopsies in 13 cases showed no extrapulmonary infected sites.
• Dominant seasonal influenza strain that cocirculated was H3N2 influenza A, but 2009 H1N1 “pushed out seasonal influenza”; 2009 H1N1 accounted for 76% of ILI patients in ICUs.

Resource List

• American College Health Association. ACHA Pandemic Influenza Surveillance. Influenza-Like Illnesses in Colleges and Universities. Available at: http://www.acha.org/ILI_surveillance.cfm Accessed October 12, 2009
• Bartlett JG, Borio L. Healthcare epidemiology: the current status of planning for pandemic influenza and implications for health care planning in the United States. Clin Infect Dis. 2008;46:919-925. Abstract
• CDC. H1N1 flu (swine flu): general information. Available at: http://www.cdc.gov/h1n1flu/general_info.htm Accessed September 16, 2009.
• CDC. Hospitalized patients with novel influenza A (H1N1) virus infection — California, April-May. MMWR Morb Mortal Wkly Rep. 2009;58:536-541. Abstract
• CDC. Intensive care patients with severe novel influenza A (H1N1) virus infection — Michigan, June 2009. MMWR Morb Mortal Wkly Rep. 2009;58:749-752. Abstract
• CDC. Interim guidance for clinicians on identifying and caring for patients with swine-origin influenza A (H1N1) virus infection. June 2009. Available at: http://www.cdc.gov/h1n1flu/identifyingpatients.htm Accessed September 16, 2009.
• CDC. Key facts about seasonal influenza (flu). Available at: www.cdc.gov/flu/keyfacts.htm Accessed September 25, 2009.
• CDC. Neurological complications associated with novel influenza A (H1N1) infection in children — Dallas, Texas, May 2009. MMWR Morb Mortal Wkly Rep. 2009;58:773-778. Abstract
• CDC Online Newsroom. Weekly 2009 H1N1 Flu Media Briefing. October 13, 2009. Available at: http://www.cdc.gov/media/transcripts/2009/t091013.htm Accessed October 14, 2009.
• CDC. Pneumonia hospitalizations among young children before and after introduction of pneumococcal conjugate vaccine — United States, 1997-2006. MMWR Morb Mortal Wkly Rep. 2009;58:1-4. Abstract
• CDC. Surveillance for the 2009 pandemic influenza A (H1N1) virus and seasonal influenza viruses — New Zealand, 2009. MMWR Morb Mortal Wkly Rep. 2009;58:918-921. Abstract
• CDC. Swine-origin influenza A (H1N1) virus infections in a school — New York City, April 2009. MMWR Morb Mortal Wkly Rep Dispatch. 2009;58:1-3. Available at: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm58d0430a1.htm Accessed September 25, 2009.
• CDC. Update: Swine-origin influenza A (H1N1) virus — United States and other countries. MMWR Wkly. 2009;58:421.
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[CLOSE WINDOW]

Authors and Disclosures

Author(s)

John G. Bartlett, MD

Professor of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland; Director, HIV Care Program, Johns Hopkins Hospital, Baltimore, Maryland Disclosure: John G. Bartlett, MD, has disclosed the following relevant financial relationships: Served on the policy board for: Johnson & Johnson Pharmaceutical Research and Development, L.L.C. Served as an advisor or consultant to: Pfizer Inc; Tibotec, Inc. Served on the data safety monitoring board for: Tibotec, Inc. Received honoraria from: Abbott Laboratories