September 23, 2004

Michigan has seen a significant increase in the number of reported cases of pertussis – also known as whooping cough – according to state public health officials.

As of the end of August 2004, 99 cases had been reported to the Michigan Department of Community Health (MDCH), with several more under investigation by local health departments throughout the state, said Janet Olszewski, MDCH Director. This level compares with 63 cases reported for the same period in 2003 – representing a 57 percent increase.

“Now, more than ever, it is vitally important to ensure that children under the age of 7 are routinely vaccinated for this disease,” Olszewski said.

Olszewski said cases of whooping cough have been reported in 30 different counties from all regions of the state. While no large outbreaks have been detected, several instances of disease clusters have been noted involving multiple cases among families, extended families, and acquaintances. Cases also have occurred in all age groups, ranging from infants as young as a few weeks old to adults.

Michigan is not unique in noting an increase in pertussis incidence. Several other states, including Wisconsin, Illinois, Ohio, Indiana, North Dakota, and New York, among others, have reported significant increases in cases this year, Olszewski said.

Pertussis infections tend to be more severe in infants and young children, who are also at an increased risk of complications associated with the disease, such as pneumonia and seizures. Pertussis can occasionally cause death. The disease tends to be less severe in adolescents and adults, often going undiagnosed in these groups. However, even in older people, pertussis can cause prolonged coughing and illness lasting several weeks.

Health experts believe that adolescents and adults with unrecognized, undiagnosed pertussis can often be the source of infections in small infants and children.

Pertussis is a vaccine preventable disease. A series of immunizations are given in the infant and childhood years. The routine schedule calls for a primary series of four doses, given at 2, 4, 6, and 15 to 18 months of age. A booster dose is given at 4 to 6 years of age.

The immunity conferred by the pertussis vaccine protects children through the early years of life, when they are most susceptible to a severe and complicated case of the disease, but this protection is believed to wear off after a period of 5 to 10 years.

One current challenge with pertussis prevention and control efforts is the fact that there is no licensed vaccine for use in persons over 7 years of age.

“Public health’s current strategy of pertussis prevention and control is to prevent cases in highly susceptible infants and young children by ensuring all doses of the pertussis vaccine series are given on time, according to the recommended childhood and adolescent immunization schedule,” Olszewski said.

While optimal immunity is not achieved until all doses in the series are administered, getting each dose of the series on time is important because it helps provide the greatest protection possible for the child’s age, she said.

Booster doses of pertussis vaccines for adolescents and adults are currently being developed and tested, but are not currently licensed for use in the U.S.

Persons with whopping cough should be treated with certain antibiotics, both to help modify the course of the illness (if given early enough) and also to limit the potential to spread the disease to others. In addition, a course of preventive antibiotic therapy is recommended for household and other close contacts of a case.

Persons diagnosed with or suspected to have pertussis should refrain from public activities, including school, child care, and the workplace, to avoid exposing others until appropriately treated with antibiotics (generally until they have completed the first 5 days of a full course of antibiotic treatment).

A general nationwide trend of increasing pertussis incidence has been observed over the past 10 to 15 years. In 2003, 11,647 cases were reported in the U.S. – the highest number reported since 1964.

The reasons for this trend are not clear. However, it is important to note that even these levels are exceedingly lower than those that occurred in the pre-pertussis vaccine era, when hundreds of thousands of cases were reported annually.

For more information about pertussis, visit the MDCH web site at www.michigan.gov/mdch or the Centers for Disease Control web site at www.cdc.gov.