Falling birth rates shift rotavirus epidemics

Jul 16, 2009

Fewer births in states such as California may be delaying the annual onset of a common intestinal virus in the southwest, according to epidemiologists. The timing of infectious outbreaks in other locations such as the northeast remains more or less unchanged.

Rotavirus is a leading cause of diarrhea among children, both in the developed and developing world. In the United States, the virus causes about 60,000 hospitalizations each year and kills about 40 children below the age of five.

"It is an imperfectly immunizing infection," said Virginia Pitzer, postdoctoral researcher in the Center for Infectious Disease Dynamics and the department of biology, Penn State. "So you can get infected multiple times throughout your life."

Up until the late 1990s, annual rotavirus in the U.S. followed a predictable pattern. Infections appeared in the southwest and peaked in December or January, then spread to the northeast, where they peaked in March. In recent years epidemics in the southwest have begun later than usual.

Pitzer and her colleagues initially looked at environmental factors such as solar radiation, precipitation and temperature but these could not explain the shifts in outbreaks of new infections. Unlike other viruses that die out and are replenished each year with new strains from outside the United States, rotavirus infections tend to linger in the summer months.

"In general, the pattern of spread of rotavirus outbreaks from the southwest to the northeast is not consistent with any climatic factors," explained Pitzer, whose findings appear today (July 17) in Science. "For instance, temperature tends to be high in the southwest but it also tends to be high in places like Florida, where epidemics occur much later."

Instead, Pitzer and her colleagues looked at human birth rates and the potential link to the timing of rotavirus epidemics. While birth rates are typically high in the southwest and low in the northeast, census data indicates a recent decline in the southwest, particularly in California.

Statistical analysis suggested a negative correlation between birth rates and the timing of the epidemics between 1991 and 2006.

"Each time there was a decline in birth rate, whether from state to state or year to year, infections tended to happen later," explained Pitzer.

A mathematical model using information on the epidemiology of rotavirus and birth rates from states confirmed the statistical correlation and predicted that given the declining birth rate in California, rotavirus epidemics in the state would gradually shift from December to February.

"Since infants often have diarrhea and can be very infectious when they get rotavirus, they are the ones who tend to drive the epidemics," said Pitzer, who is also associated with Fogarty International Center at the National Institutes of Health through the Research and Policy for Infectious Disease Dynamics program. "Thus, you can get outbreaks of rotavirus happening a lot sooner when and where there are more infants being born."

Vaccines introduced in 2006 further confirm Pitzer's model. Since vaccination reduces the number of infants vulnerable to symptomatic infections, the effect is analogous to a decline in birth rate.

"With the effects of vaccination factored in, the model accurately predicted a small decrease in the incidence of severe diarrhea during the 2006-2007 season, and a larger decline and delay during 2007-2008, providing validation for our model," said Pitzer.

Researchers add that high levels of vaccination could further limit the intensity of new epidemics and lead to a period of years with very few cases of severe caused by rotavirus.

"The important message here is that vaccination can have a big impact in controlling rotavirus infections," explained Pitzer. "Even those not vaccinated can benefit from those vaccinated because it lowers the overall prevalence of the infection in the population."

Source: Pennsylvania State University (news : web)

Explore further: Volunteer guidelines for clinicians in the Ebola epidemic

add to favorites email to friend print save as pdf

Related Stories

Rotavirus can spread beyond the intestine

Apr 17, 2007

A new study in PLoS Medicine has shown that children who have rotavirus, a very common cause of diarrhea in children, and who have antigens (protein fragments from the surface of the virus) in their blood, also have infect ...

Dry season brings on measles in sub-Saharan Africa

Feb 06, 2008

Measles epidemics in Niger fluctuate wildly from one season to another but the timing of the outbreaks always coincides with the end of the annual rainy season, according to an international team of researchers.

Researchers find chink in the armor of viral 'tummy bug'

Dec 23, 2008

Researchers at Griffith University's Institute for Glycomics in collaboration with colleagues at the University of Melbourne have moved a step closer to identifying a broad spectrum treatment for the dreaded 'viral tummy ...

Study uncovers cause of flu epidemics

Mar 04, 2008

The exchange of genetic material between two closely related strains of the influenza A virus may have caused the 1947 and 1951 human flu epidemics, according to biologists. The findings could help explain why some strains ...

Recommended for you

Volunteer guidelines for clinicians in the Ebola epidemic

5 minutes ago

Disaster Medicine and Public Health Preparedness Journal has released a novel, informative article that speaks to volunteers within the Ebola epidemic. The article, contributed by a consortium of Boston-based hospitals, is ent ...

US lawmaker: New case raises questions on Ebola

1 hour ago

The new case of Ebola diagnosed in New York City has raised "even more questions about procedures in treating patients and risks to Americans," a Republican committee chairman said Friday.

Aid group: Ebola contagion risk can't be zero

1 hour ago

Despite stringent infection-control measures, the risk of Ebola's spread cannot be entirely eliminated, Doctors Without Borders said Friday after one of its doctors caught the dreaded disease while working in Guinea and went ...

WHO eyes mass Ebola vaccines by mid-2015

1 hour ago

Hundreds of thousands of Ebola vaccine doses could be rolled out to west Africa by the middle of next year, the World Health Organization said Friday, after new cases of the killer virus were reported in New York and Mali.

User comments : 0