Novel H1N1 Influenza

www.cdc.gov/H1N1flu

Novel H1N1 Influenza

• The United States Government has declared a public health emergency in the United States in response to this novel H1N1 Influenza. CDC’s response goals are to reduce transmission and illness severity, and provide information to help health care providers, public health officials, and the public address the challenges posed by this emergency.

www.cdc.gov/H1N1flu

Novel H1N1 Influenza (continued)

In late March and early April 2009, cases of human

infection with a novel H1N1 influenza virus were first

reported in Southern California and near

Guadalupe County, Texas. Other U.S. states have

reported cases of swine flu infection in humans and

cases have been reported internationally as well.

www.cdc.gov/H1N1flu

Novel H1N1 Influenza (continued)

Deaths associated with this outbreak of the novel

H1N1 influenza have been reported in Mexico and the

United States. Hundreds of cases have been reported

by other countries. CDC expects the number of cases

and deaths to increase.

www.cdc.gov/H1N1flu

Pandemic LevelsThe World Health Organization uses a six-phased

approach for easy incorporation of new

recommendations and approaches into existing

national preparedness and response plans.

www.cdc.gov/H1N1flu

What are the symptoms?The symptoms of this novel H1N1 Influenza

(formerly referred to as swine flu) in people are

similar to the symptoms of regular human flu and

include fever, cough, sore throat, body aches,

headache, chills and fatigue. Some people have

reported diarrhea and vomiting.

www.cdc.gov/H1N1flu

How Influenza Viruses Spread

• Primarily through respiratory droplets

– Coughing

– Sneezing– Touching respiratory droplets on

self, another person, or an object, then touching mucus membranes (e.g., mouth, nose, eyes) without washing hands

www.cdc.gov/H1N1flu

Is this a pandemic?

During a regular flu season in the United States, we anticipate

• >200,000 hospitalizations / year

• 36,000 deaths / year

• Substantial economic impact ~$37.5 billion in economic costs and pneumonia

www.cdc.gov/H1N1flu

Is this a pandemic (continued)?

An influenza pandemic is a global outbreak of disease

that occurs when:• A new influenza A virus appears or “emerges” in

the human population, and• It causes serious illness in humans, and• It spreads easily from person to person worldwide

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Global cases as of May 6, 09

www.cdc.gov/H1N1flu

Situation reports: USA

As of May 6, 2009• 642 cases in 41 states (a lot of this due to samples

finally getting tested)• 845 probable cases in those 42 states. Over 90%

turn out to be confirmed so expect case counts to go up a lot.

• 35 hospitalizations in confirmed cases (4.7% of confirmed and probable) – evolving rapidly

• Attack rate ~ 22% (seasonal flu 5-20%)

www.cdc.gov/H1N1flu


• 2 deaths. The 2nd case is the first American to die of this infection

• All cases: median age 16 yrs (3 months – 81 years). 62% under 18

• 1/3 of confirmed cases have some link to Mexico but most do not

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• Still detecting a fair amount of seasonal flu, mostly H3N2 May be due to heightened surveillance ILI visits above threshold that normally

designates an influenza system• Mortality data has also increased slightly

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Lab looking at cross protective antibodies• Older adults may have antibodies with some

cross protection• This is just in vitro data so far• Children have little in the way of antibodies that

might be cross protective• Prevalence of potentially cross protective

antibodies increases with age

www.cdc.gov/H1N1flu


• To date, all tested viruses were resistant to Amantadine and Rimantadine, but susceptible to Oseltamivir and Zanamivir

www.cdc.gov/H1N1flu

Use of Rapid Influenza Diagnostic Tests for Patients with ILI during Novel H1N1 outbreak

• Data are not yet available to inform recommendations on the use• It is reasonable to assume that rapid tests that detect Flu A viral

nuceoprotein antigen can detect novel H1N1 in respiratory specimens

• Sensitivity & specificity on H1N1 is not yet known• Data subsequently shown here are anecdotal• Clinicians may consider using rapid tests as part of their clinical

evaluation of patients, but results should be interpreted with caution.

• Positive from rapid tests must be confirmed by RT-PCR or viral culture

www.cdc.gov/H1N1flu


• Reliability of rapid tests depends largely on the conditions under which they are used, and are entirely based on experiences with seasonal flu

• For seasonal flu, sensitivity ~ 50-70% when compared to RT-PCR or viral culture, but specificity ~ 90-95%

• False-positive and true-negative results are more likely to occur when flu is uncommon in the community, typically at the beginning or the end of an outbreak

• False-negative and true-positive results are more likely to occur when flu is common in the community, typically at the height of an outbreak

• Sensitivity varies depending on when in the course of illness the specimen is collected. Specimens collected during the first 4-5 days of illness is greatest.

www.cdc.gov/H1N1flu


How to interpret a positive test• A patient with a positive test for flu B likely infected with

seasonal flu B or is a false positive result. Such patient is unlikely to have infection with novel H1N1.

• Several possibilities when a patient tests +ve for flu A– Might have novel H1N1– Might have seasonal flu A or– Might have a false positive result

www.cdc.gov/H1N1flu


How to interpret a negative test• H1N1 flu infection cannot be excluded when a patient tests

negative for flu A by rapid test.• If a patient has an epidemiologic link to a confirmed case, or has

either traveled to or resides in an area where there are one or more confirmed H1N1 cases, further testing and treatment should be based upon clinical suspicion, severity of illness, and risk for complications.

• If a patient has mild illness and no epidemiologic link, further testing and treatment are not recommended

www.cdc.gov/H1N1flu

Investigations of H1N1 infections in a school – NYC

• On Apr 24, 09, CDC reported 8 confirmed cases of novel H1N1 virus infection in Texas & California

• The strain identified in U.S. patients was confirmed as genetically similar to viruses subsequently isolated from patients in Mexico

• To date, confirmed cases among students and staff member of a New York City (NYC) school remain a large proportion of confirmed patients in the U.S.

Source: MMWR April 30, 2009 / Vol. 58 / Dispatch - Swine-Origin Influenza A (H1N1) Virus Infections in a School — New York City, April 2009 (http://www.cdc.gov/mmwr/pdf/wk/mm58d0430.pdf)

www.cdc.gov/H1N1flu

Investigation of H1N1 infections in a school – NYC

• Apr 23, 09 – NYC health department was notified of ~ 100 cases of mild (uncomplicated) respiratory illness among students at a high school in NYC with 2,686 students and 228 staff members

• During Apr 23-24, a total of 222 students visited the school nursing office and left school

• NYC health department mobilized officers to go and collect nasopharyngeal swab from symptomatic students at the school and from students absent due to illness

www.cdc.gov/H1N1flu


• Decision was made not to open the school the following week

• Contact and suspected cases in neighborhood also had NP swab collected

• 44 cases out of 53 tested positive for novel H1N1• Telephone interview with 44 confirmed cases was

conducted

www.cdc.gov/H1N1flu


Characteristic N = 44

Median age 15 (range: 14-21) Students All but one student teacherSex 31 (70%) were female

Race - Non-Hispanic white - Hispanic - non-Hispanic black - others

30 (68%)7 (16%)2 (5%)5 (11%)

Travel None reported recent travel to CA, TX, or Mexico (Several students participating in the separate on-line survey reported travel to Mexico. None had confirmed H1N1 by PCR.)

www.cdc.gov/H1N1flu

Investigation of H1N1 infections in a school – NYCCharacteristic N = 44

Illness onset Apr 20 – 24 (see Epi curve)

Symptoms- Cough- Fever- Fatigue- Headache- Sore throat- Runny nose- Chill- Muscle ache- Nausea- Stomach ache- Diarrhea- Shortness of breath- Joint pain

43 (98%)42 (96%)39 (89%)36 (82%)36 (82%)36 (82%)35 (80%)35 (80%)24 (55%)22 (50%)21 (48%)21 (48%)20 (46%)

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Epidemic curve: Outbreak in NYC school

Number of confirmed cases (N=45) of novel Flu A (H1N1) virus infection in a school, by date of illness onset, April 2009

www.cdc.gov/H1N1flu

Investigation reports: International

• Reports from Mexico suggest that epidemic curve might be flattening there

• Studies – spectrum of illness, community transmission, clear clinical description

• Spectrum of disease: Trying to do community survey in a place where denominator can be defined – serosurvey

www.cdc.gov/H1N1flu

Surveillance transition in US

– State reporting• From line list to aggregate report: total cases, deaths,

hospitalizations• Move toward population-based surveillance: existing

surveillance systems, random sample surveys – Laboratory

• Moving to being done at state labs confirmation testing of 2009-H1N1

– Assessing cases in specific population cases: pediatric, maternal and infant, and health care workers (important for severity & future vaccine considerations)

www.cdc.gov/H1N1flu

Summary• Human infections with a novel Influenza A (H1N1)

virus have been documented in multiple countries around the globe

• Virus was first identified in North America; currently few confirmed cases to in East Asia

• High proportion of cases in young adults and children

• Clinical spectrum still not well-defined but early cases suggest clinical course similar to seasonal influenza

www.cdc.gov/H1N1flu

Final notes• Because this is a new virus, most people will not have

immunity and illness may be more widespread• Therefore, it is important to prepare for the potential of a

large number of persons becoming ill and the impact on• Workforce, including health care workers• Health care services (e.g., hospital beds, ventilators)• Public works (e.g., water, sewer, transportation)• Socio-economic issues

• Thailand and other countries in this region are fortunate that the outbreak started in North America and we have a short window of time to prepare

www.cdc.gov/H1N1flu

Resources

• For the most current information on the H1N1 influenza outbreak, visit http://www.cdc.gov/h1n1flu/

• http://www.pandemicflu.gov/• http://www.who.int/csr/disease/swineflu/en/index.html• http://www.cdc.gov/mmwr/• Some useful guidance can be retrieved at

http://www.cdc.gov/h1n1flu/guidance/, includes clinician guidance for patients, treatment, screening & specimen collection, laboratories, guidance for schools and university, guidance for pregnant and breastfeeding women, and travel guidance

Documents

Novel H1N1 Influenza