Pertussis incidence: an interview with Leonard Friedland, M.D., V.P. and Director of Scientific Affairs and Public Health for GSK Vaccines

Interview conducted by April Cashin-Garbutt, MA (Editor)Oct 24 2013

Why have infectious disease experts long suspected that pertussis cases in adults may be greatly under-reported?

Distinguishing pertussis (also known as whooping cough) from other respiratory illnesses is challenging in particular among adults because the signs and symptoms of pertussis overlap with those of other respiratory diseases. Clinicians often are not fully aware of the prevalence of pertussis among older adults.

A recent GSK study also signals that pertussis incidence increased over the years. In 2010, the estimated incidence was 292 per 100,000 for people aged 50-64 and 464 per 100,000 for people > 65. These were 94 and 264 times higher than CDC national reported incidences for individuals aged 40-65 and ≥65 years, respectively.

What makes pertussis difficult to diagnose and why is it often misdiagnosed as other respiratory ailments?

The signs and symptoms of pertussis overlap with those of other respiratory diseases. Clinicians often are not fully aware of prevalence of pertussis among older adults.

Please can you outline the recent study conducted by GlaxoSmithKline researchers into the incidence of pertussis among U.S. adults over 50?

GSK researchers analyzed approximately 48 million cases of cough-related illness in the U.S. between 2006 and 2010, and presented the findings at the 2013 Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).

We believe this is the first time a mathematical model (multiple linear regression) has been applied to estimate the real number of pertussis cases among older adults in the U.S using a database that represents the whole U.S. This methodology has been used extensively to estimate the burden of other underreported diseases that are rarely confirmed by laboratory testing, such as influenza.

• GSK utilized data from the IMS private practice database that included more than 80 million claims per year. The commercial laboratory testing database represents approximately 40 percent of respiratory-laboratory testing that took place in the U.S. during the years looked at in the study.

Why did the study only focus on adults over 50?

Within the past few years, there has been a growing consensus in the medical community of the need for adults to receive Tdap, if they will be in close contact with infants 12 months of age or less. These adults include grandparents or caregivers over the age of 50.

This growing medical need presented an opportunity – and GSK believes it’s the first - to attempt to quantify the incidence of cough illness attributed to B. pertussis via regression modeling among those adults greater than 50 years old.

What were the key findings of this study and how did they compare to the previously reported pertussis incidences?

Key study findings included:

• The actual number of pertussis cases among U.S. adults ages 50 to 65 was approximately 520,000 vs. the 8,764 medically-attended cases documented by the U.S. Centers for Disease Control (CDC).
• Among adults 65 and older, the GSK study results suggested approximately 465,000 cases of pertussis occurred, a figure well above the 6,359 medically-documented cases.
• The findings also signal that pertussis incidence increased over the years. In 2010, the estimated incidence was 292 per 100,000 for people aged 50-64 and 464 per 100,000 for people > 65. These were 94 and 264 times higher than CDC national reported incidences for individuals aged 40-65 and ≥65 years, respectively.

What are the main limitations of this research and how does this affect the way the results should be interpreted?

The results of this study should be interpreted in the context of its limitations. Claims data are inherently limiting, because they are collected for billing and reimbursement purposes rather than for research.

Only patients seeking medical attention from private practitioners and only positive B. pertussis laboratory tests were included.

Lastly, the incidence of cough attributed to B. pertussis was based on mathematical modelling. Models try to mimic the reality and are subject to numerous limitations and assumptions.

What impact do you think this study will have on the diagnosis of pertussis going forwards?

The authors plan to share their research methods and welcome other researchers to further examine and build upon the findings of this study. These findings suggest a major need for healthcare providers to consider the possibility of pertussis in older patients they see who have respiratory symptoms.

How can the identification of pertussis be improved?

The findings of the GSK study support that a need exists to develop clinical approaches and public health programs to curb the spread of pertussis among older adults. Distinguishing pertussis from other respiratory illnesses is challenging in particular among adults because the signs and symptoms of pertussis overlap with those of other respiratory diseases.

Clinicians often are not fully aware of prevalence of pertussis among older adults. Clinicians should consider the possibility of pertussis in older patients they see who have respiratory symptoms. In addition, adults 50 and over should be aware of the signs and symptoms of pertussis, and report them to their healthcare providers.

Signs and symptoms can be found on the CDC’s Web site http://www.cdc.gov/pertussis/about/signs-symptoms.html.

Where can readers find more information?

The CDC has developed and published a comprehensive pertussis guide that can be accessed at https://www.cdc.gov/

About Leonard Friedland

Leonard Friedland, MD, is a pediatrician and pediatric emergency medicine trained physician, and vaccine research scientist.

Leonard is a graduate of Vassar College and Mount Sinai School of Medicine. His residency and fellowship training was in Philadelphia at Children’s Hospital of Philadelphia and St. Christopher’s Hospital for Children.

He was on staff at Cincinnati Children’s Hospital Medical Center (Assistant Professor) and Temple University Children’s Hospital (Associate Professor) before joining GlaxoSmithKline Biologicals in 2003.

Leonard currently is Vice President and Director of Scientific Affairs and Public Health, Vaccines in North America at GSK.  He has been involved with the development of many vaccines currently recommended for use in infants, children, adolescents, adults and the elderly.