Study: Quantifying H1N1 Risk Factors

 

 

# 4419

 

From almost the start of the pandemic of 2009 we heard warnings and anecdotal stories about specific risk factors that predisposed some people towards hospital and/or ICU admissions when stricken by the H1N1 swine flu virus.

 

In late May, weeks before the pandemic was officially declared, I posted the following list from the CDC of those believed to be at higher risk from this, and other, influenza viruses.

 

 

Groups at Higher Risk for Severe Illness from Novel Influenza A (H1N1) Infection

Groups of people at higher risk for severe illness from novel influenza A (H1N1) infection are thought to be the same as those people at higher risk for severe illness from seasonal influenza. These groups include:

• Children younger than 5 years old
• Persons aged 65 years or older
• Children and adolescents (younger than 18 years) who are receiving long-term aspirin therapy and who might be at risk for experiencing Reye syndrome after influenza virus infection
• Pregnant women
• Adults and children who have pulmonary, including asthma, cardiovascular, hepatic, hematological, neurologic, neuromuscular, or metabolic disorders such as diabetes
• Adults and children who have immunosuppression (including immunosuppression caused by medications or by HIV)
• Residents of nursing homes and other chronic-care facilities.

 

Pregnancy was an important risk factor in the 1918 Spanish Flu, and again during the 1957 pandemic, so concerns over it (and other risk factors) formed the basis for a good deal of discussion over the summer.  A few examples include:

 

Pregnancy & Flu: A Bad Combination

WHO Pandemic Briefing # 5: Influenza In Pregnant Women

Lancet Study: Pregnancy And H1N1

 

 

While it may take years before we understand – with any precision – the full impact of this pandemic, we are seeing more post-pandemic-wave analyses being published, such as this one from PLoS Currents Influenza entitled:

 

 

Preliminary estimation of risk factors for admission to intensive care units and for death in patients infected with A(H1N1)2009 influenza virus, France, 2009-2010

To estimate the magnitude of the risks associated with age, obesity, pregnancy and diabetes, we compared the prevalence of these conditions reported in hospitalized severe cases to that in the general population, during the 2009-2010 A(H1N1) pandemic flu in France.

 

Pregnancy, obesity, heart failure and diabetes were risk factors for admission into an intensive care unit (OR=5.2 [95%CI 4.0-6.9], 3.8 [3.0-4.9], 3.3 [2.6-4.1] and 2.8 [2.3-3.4], respectively).

 

Only heart failure, obesity, and diabetes were significantly associated with death (OR=6.9 [4.9-9.8], 3.6 [1.9-6.2], and 3.5 [2.5-5.1], respectively). Elderly adults were at lower risk of being admitted into an ICU, but at higher risk of death.

 

 

A word of caution. 

 

This study looked at five specific risk groups; age, diabetes, pregnancy, obesity, and heart failure and not at the full gamut of H1N1 hospitalization risk factors.  

 

You’ll find no mention of Asthma, COPD, or Neuro/ Developmental disorders – all of which have been linked to higher rates of H1N1 hospitalization in other studies.

 

And so this data must be viewed in that limited context.

 

Over time, studies such as this one – when combined with dozens of others – will help us understand how the pandemic of 2009 affected the world.    

 

Some of the other hospitalization studies we’ve seen over the past few months include:

 

CDC Q&A On H1N1 And Underlying Conditions

CMAJ: Asthma As A Pandemic Risk Factor In Children

Australian Study: H1N1 Hospitalized Patients

Study: H1N1 Hospitalization Profiles

Study: H1N1 A Threat To All Age Groups

 

No doubt we’ll see dozens more over the coming months. 

CIDRAP: Pediatric Hospitals Faced Tough Choices

 

 

# 4225

 

 

The pandemic of 2009, while not exactly a Stephen King scale catastrophe, most certainly presented challenges to the medical community.  Emergency rooms, ICUs, and pediatric hospitals were heavily impacted during the recent fall wave.

 

Lisa Schnirring of CIDRAP News has a detailed look at how the pandemic preparedness team at Children's Hospitals and Clinics of Minnesota dealt with the crisis.

 

This is not only a good read, it is an important reminder that the H1N1 virus levied a heavy burden at times on patients, their families, and on the medical community tasked with caring for them.

 

Follow the link to read the article in its entirety.

 

 

Fall flu wave tested pediatric hospitals with tough choices

 

Lisa Schnirring Staff Writer

Jan 5, 2010 (CIDRAP News) – In early August 2009, when the pandemic virus started tearing through southern states where schools had already started, the pandemic preparedness team at Children's Hospitals and Clinics of Minnesota felt a sense of foreboding that the virus was poised to strike the area a second time.

 

Pediatric hospitals throughout the United States have been at ground zero during both waves of the pandemic. The patients they care for are among the groups at highest risk for complications from the pandemic virus—young people with chronic health conditions such as asthma, diabetes, neuromuscular disorders, and forms of cancer.

 

Throughout the pandemic, communities have relied heavily on children's hospitals as high-profile sources of flu information. When the vaccine made its debut in October, public health officials took advantage of such hospitals' unique ability to reach many of the highest-risk groups with the first doses.

 

(Continue . . . )

CMAJ: Asthma As A Pandemic Risk Factor In Children

 

 

# 4045

 

A study led by Toronto researchers at the the Hospital For Sick Children (Sickkids) has been published today in the CMAJ, the Journal of the Canadian Medical Association, that looks at pediatric hospital admission during the opening months of this pandemic.

 

The study examine the charts of 58 kids admitted with H1N1 between May 8th and July 22nd, and compared those against roughly 200 admissions for seasonal flu over the past 5 years.   

 

In an average year, the hospital admits about 40 pediatric influenza patients, so the admission of 58 kids in just 10 weeks alone is illustrative that this year is different.

 

Among other things, the study found.

 

• With seasonal flu, roughly 6% of the patients admitted had a history of asthma, whereas with the novel H1N1 virus, that number was 22% (13 of 58).
• Almost half of the kids sick enough to be admitted to the ICU had a history of asthma.
• Additionally, the median age of kids admitted for H1N1 was nearly twice that of kids admitted in previous years for seasonal flu.

 

The study is available online.

 

Risk factors and outcomes among children admitted to hospital with pandemic H1N1 influenza

Sean O’Riordan MB BChir PhD, Michelle Barton MBBS DM, Yvonne Yau MD, Stanley E. Read MD PhD, Upton Allen MBBS MSc, Dat Tran MD MSc

Background: Limited data are available on disease characteristics and outcomes of children with 2009 pandemic influenza A(H1N1) virus infection (pandemic H1N1 influenza)who have required hospital admission.

Methods: We reviewed the charts of 58 children with pandemic H1N1 influenza admitted to a large pediatric hospital in Ontario, Canada, between May 8 and July 22, 2009. We compared risk factors, severity indicators and outcomes of these children with those of 200 children admitted with seasonal influenza A during the previous 5 years (2004/05 to 2008/09).

Results: Children with pandemic H1N1 influenza were significantly older than those with seasonal influenza (median age 6.4 years v. 3.3 years). Forty-six (79%) of the children with pandemic H1N1 influenza had underlying medical conditions; of the other 12 who were previously healthy, 42% were under 2 years of age.

 

Children admitted with pandemic H1N1 influenza were significantly more likely to have asthma than those with seasonal influenza (22% v. 6%). Two children had poorly controlled asthma, and 6 used inhaled medications only intermittently. The median length of stay in hospital was 4 days in both groups of children.

 

Similar proportions of children required admission to the intensive care unit (21% of those with pandemic H1N1 influenza and 14% of those with seasonal influenza) and mechanical ventilation (12% and 10%respectively). None of the children admitted with pandemic H1N1 influenza died, as compared with 1 (0.4%) of those admitted with seasonal influenza.

Interpretation: Pandemic H1N1 influenza did not appear to cause more severe disease than seasonal influenza A. Asthma appears to be a significant risk factor for severe disease, with no clear relation to severity of asthma. This finding should influence strategies for vaccination and pre-emptive antiviral therapy

CDC Releases Revised Hospitalization & Death Estimates

 

# 4002

 

 

Just posted on the CDC website, the long awaited estimates of the impact of the H1N1 pandemic in the United States.   These numbers are through Oct 17th.

 

These are not actual counts, but a range of estimates.   We simply lack the surveillance and reporting ability to count influenza-related deaths in this country.   

 

You can find previous discussions on the reasons why the official counts under represent the true number of cases, hospitalizations, and deaths at:

 

When No Number Is Right

Dead Reckoning

Numbers Don’t Tell The Whole Story

A Decided Lack Of Data

Measuring The Severity Of A Pandemic

Arizona & Illinois Report Swine Flu Related Deaths

 

The following are excerpts from a much larger web page explaining how the CDC derived these numbers.   Follow the link to read it in its entirety.

 

 

CDC Estimates of 2009 H1N1 Influenza Cases, Hospitalizations and Deaths in the United States, April – October 17, 2009

November 12, 2009, 1:00 PM ET

The Numbers

• CDC estimates that between 14 million and 34 million cases of 2009 H1N1 occurred between April and October 17, 2009. The mid-level in this range is about 22 million people infected with 2009 H1N1.
• CDC estimates that between about 63,000 and 153,000 2009 H1N1-related hospitalizations occurred between April and October 17, 2009. The mid-level in this range is about 98,000 H1N1-related hospitalizations.
• CDC estimates that between about 2,500 and 6,000 2009 H1N1-related deaths occurred between April and October 17, 2009. The mid-level in this range is about 3,900 2009 H1N1-related deaths.

Under-Counting of Flu-Related Deaths

CDC does not know exactly how many people die from seasonal flu each year. There are several reasons for this:

• First, states are not required to report individual seasonal flu cases or deaths of people older than 18 years of age to CDC.
• Second, seasonal influenza is infrequently listed on death certificates of people who die from flu-related complications.
• Third, many seasonal flu-related deaths occur one or two weeks after a person’s initial infection, either because the person may develop a secondary bacterial co-infection (such as a staph infection) or because seasonal influenza can aggravate an existing chronic illness (such as congestive heart failure or chronic obstructive pulmonary disease).
• Also, most people who die from seasonal flu-related complications are not tested for flu, or they seek medical care later in their illness when seasonal influenza can no longer be detected from respiratory samples. Influenza tests are most likely to detect influenza if performed soon after onset of illness.
• For these reasons, many flu-related deaths may not be recorded on death certificates.

These are some of the reasons that CDC and other public health agencies in the United States and other countries use statistical models to estimate the annual number of seasonal flu-related deaths. (Flu deaths in children were made a nationally notifiable condition in 2004, and since then, states have reported flu-related child deaths in the United States through the Influenza Associated Pediatric Mortality Surveillance System).

Study: H1N1 Hospitalization Profiles

 

 

# 3982

 

 

As we get deeper into this pandemic, we are getting more studies from around the world on the types of patients most likely to be hospitalized, and their lengths of stay.  

 

While there may be some variations in patient profiles from around the world, asthma continues to be one of the biggest risk factors, generally followed by chronic respiratory disease and immunosuppression.

 

From Eurosurveillance we get a study out of Ireland, based on more than 200 hospitalizations between April and October of this year, that gives us some badly needed detail on hospitalized patient profiles.

 

While comorbid conditions such as asthma obviously play a part, it should be noted that slightly more than half of those hospitalized fell into no recognized risk group.

A few excerpts from the study below:

 

Eurosurveillance, Volume 14, Issue 44, 05 November 2009

Rapid communications

Surveillance of the first 205 confirmed hospitalised cases of pandemic H1N1 influenza in Ireland, 28 April – 3 October 2009

G Cullen, J Martin , J O’Donnell, M Boland, M Canny, E Keane, A McNamara, A O’Hora, M Fitzgerald, S Jackson, D Igoe, D O’Flanagan

From 28 April 2009 to 3 October 2009, 205 cases of confirmed pandemic H1N1 influenza were hospitalised in Ireland. Detailed case-based epidemiological information was gathered on all hospitalised cases.

 

Age-specific hospitalisation rates were highest in the age group of 15 to 19 year-olds and lowest in those aged 65 years and over.

 

Nineteen hospitalised cases (9%) were admitted to intensive care units (ICU) where the median length of stay was 24 days. Four hospitalised cases (2%) died.

 

Fifty-one percent of hospitalised cases and 42% of ICU cases were not in a recognised risk group. Asthma was the most common risk factor among cases; however, people with haemoglobinopathies and immunosuppression were the most over-represented groups.

 

 

From the Irish Examiner, a good synopsis of the above study.   I’ve excerpted some passages, but follow the link to read it in its entirety.

 

 

 

Asthma medication is most common swine flu ‘risk factor’

By Catherine Shanahan

Tuesday, November 10, 2009

BEING on medication for asthma is the most common risk factor for hospitalisation due to swine flu, according to a study of the first 205 pandemic patients admitted to Irish hospitals.

 

The assessment also found hospitalisation rates have been shifting to younger age groups, with the highest rate initially in teenagers and currently in children under five years.

 

The analysis of data by members of the Health Protection Surveillance Centre and public health doctors in the HSE, revealed that:

• After asthma, the most common risk factors for hospitalisation were chronic respiratory disease and immunosuppression (where the immune system is suppressed due to illness).
• The most common risk factor in admission to intensive care was chronic respiratory disease followed by chronic neurological disease, asthma and severe obesity.
• Pneumonia was the most common complication. Of 40 patients that developed pneumonia, just 17 were in a risk group.
• Hospitalisation rates were lowest in the over 65.
• 51% of hospitalised cases and 42% of ICU cases were not in a recognised risk group.

<SNIP>

The median length of stay in hospital was two days for cases under the age of 24 years but increasing to seven days in adults over 65 years. Asthma was associated with a mean length of stay of six days. 

 

(Continue . . . )

NEJM: Review Of Hospitalized US Patients With Novel H1N1

 

# 3816

 

 

Tonight Maggie Fox of Reuters brings us an excellent overview of a new study, published today in the NEJM, which confirms just how hard the novel H1N1 virus has hit younger patients.

 

Unlike seasonal flu, which is most devastating to those over 65, this novel swine flu virus has a predilection for the young.  Ninety-five percent of the patients hospitalized included in this study were under the age of 65 and 45% were under the age of 18.

 

One of the other unusual aspect to this flu is the high percentage of vomiting and diarrhea reported.  The early application of antivirals was seen to be therapeutic, and once again the question of morbid obesity being a serious complicating factor is raised.

 

First the Reuters report, then a link to the study.  Follow the link below to read the entire article.

 

US flu study confirms H1N1 more serious in youth

Thu Oct 8, 2009 10:41pm BST

* 45 percent of those hospitalized were under 18

* Diarrhea, vomiting in 42 percent of children with H1N1

* Quick drug treatment may save lives

By Maggie Fox, Health and Science Editor

WASHINGTON, Oct 8 (Reuters) - A study of people who became seriously ill and died with the new pandemic swine flu confirms it is hitting a younger population than the seasonal flu and causes often different symptoms.

 

The study of 272 patients sick enough to be hospitalized showed about 40 percent had diarrhea and vomiting -- usually rare with seasonal flu -- and confirmed that quick treatment with antivirals could save lives.

 

Dr. Seema Jain of the U.S. Centers for Disease Control and Prevention, who led the study, said the findings had informed the CDC's advice on who should worry about the new H1N1 virus and when to get treatment.

(Continue . . . )

 

 

 

Published at www.nejm.org October 8, 2009 (10.1056/NEJMoa0906695)

Hospitalized Patients with 2009 H1N1 Influenza in the United States, April–June 2009

N Engl J Med 2009 0: NEJMoa0906695

Jain, Seema, Kamimoto, Laurie, Bramley, Anna M., Schmitz, Ann M., Benoit, Stephen R., Louie, Janice, Sugerman, David E., Druckenmiller, Jean K., Ritger, Kathleen A., Chugh, Rashmi, Jasuja, Supriya, Deutscher, Meredith, Chen, Sanny, Walker, John D., Duchin, Jeffrey S., Lett, Susan, Soliva, Susan, Wells, Eden V., Swerdlow, David, Uyeki, Timothy M., Fiore, Anthony E., Olsen, Sonja J., Fry, Alicia M., Bridges, Carolyn B., Finelli, Lyn, the 2009 Pandemic Influenza A (H1N1) Virus Hospitalizations Investigation Team,

ABSTRACT (Excerpts)

Background During the spring of 2009, a pandemic influenza A (H1N1) virus emerged and spread globally. We describe the clinical characteristics of the patients who were hospitalized with 2009 H1N1 influenza in the United States from April 2009 to mid-June 2009.

 
<SNIP>

 

Results Of the 272 patients we studied, 25% were admitted to an intensive care unit and 7% died. Forty-five percent of the patients were children under the age of 18 years, and 5% were 65 years of age or older. Seventy-three percent of the patients had at least one underlying medical condition; these conditions included asthma; diabetes; heart, lung, and neurologic diseases; and pregnancy.

 

Of the 249 patients who underwent chest radiography on admission, 100 (40%) had findings consistent with pneumonia. Of the 268 patients for whom data were available regarding the use of antiviral drugs, such therapy was initiated in 200 patients (75%) at a median of 3 days after the onset of illness. Data suggest that the use of antiviral drugs was beneficial in hospitalized patients, especially when such therapy was initiated early.

 

Conclusions During the evaluation period, 2009 H1N1 influenza caused severe illness requiring hospitalization, including pneumonia and death. Nearly three quarters of the patients had one or more underlying medical conditions. Few severe illnesses were reported among persons 65 years of age or older. Patients seemed to benefit from antiviral therapy.