Nancy A. Melville

May 14, 2012

May 14, 2012 (Thessaloniki, Greece) — Infants with pertussis and high or rapidly increasing white blood cell (WBC) counts are more likely to become critically ill than those with lower counts, according to research presented here at the European Society for Paediatric Infectious Diseases 30th Annual Meeting.

Pertussis was the cause of death of 10 infants during an epidemic in California in 2010. Data on the most appropriate management of pertussis, however, are limited.

The researchers evaluated data on infants 90 days and younger who were admitted to 1 of 5 pediatric intensive care units (ICUs) in California with pertussis from September 2009 to June 2011.

Of the 31 infants admitted during that period (55% female, 94% Hispanic), 8 had very severe infections. Of the 8, 7 had pulmonary hypertension and 4 died.

Infants with severe illness were not demographically dissimilar from those with less severe illness, and there were no significant differences in time from initial illness onset to the time of medical care.

There were significant differences in WBC counts, however. Those with more severe infections had higher peak WBC counts (74,200 vs 26,900; P < .01), and their WBC exceeded 30,000 more rapidly after illness onset (5.1 vs 14.6 days; P < .01).

"The means and medians for WBC counts were higher in the infants with more severe disease — all were over 30,000. The important thing is not just that they were high, but that they got there quicker," said coauthor James D. Cherry, MD, MSc, professor of pediatrics at the David Geffen School of Medicine and the Mattel Children's Hospital at the University of California at Los Angeles.

"The mean [time to elevated WBC] was 5 days for those with severe disease, compared with 22 days in the less severe group, and 50% of those with severe disease had a 50% increase within 24 hours," he said.

Heart rate measurements were also higher, and increased heart rates emerged faster with more severe disease than with less severe disease (6.0 vs 10.9 days), Dr. Cherry reported.

Respiratory rates were also higher. "Those with pulmonary hypertension who died all had a rate greater than 70 per minute; again, the slope of getting there was much quicker," Dr. Cherry said.

Those with severe disease all developed pneumonia and did so sooner. Factors that did not show significant differences included blood pressure and oxygen saturation, he noted.

The study was originally designed to compare the use of exchange transfusion in such patients at 5 centers. One of the centers could not participate, however, so the study instead focused on and gathered other data, but Dr. Cherry explained that exchange transfusion is still an important issue.

"Virtually all infant pertussis deaths are associated with extreme leukocytosis. The reason I think you should do exchange is to remove toxins beyond what can be accomplished with just filtration," he said.

"Our experience with exchange transfusion is that, for instance, with a 50,000 WBC count, you'd bring it down to 20,000 or so with a double volume exchange. Sometimes that's all that's necessary, but I've seen several cases where it went back up again and you need another transfusion."

Too often, however, the treatment isn't provided in time, with disastrous consequences, Dr. Cherry added.

"Our experience is that people in the ICU procrastinate on the transfusion; by the time they do it, there is already renal failure or shock, and then it's too late," he said.

"If we're going to save babies, we need to do white blood cell counts, even when they don't look very ill. We need to do pulse and respiratory rates as well, and if they are rising like this, these patients should be in ICUs and, in my view, they should get an exchange transfusion."

This study sheds light on several issues involving infant pertussis, noted Ronald de Groot, MD, from the division of pediatric infectious diseases at Radboud University Nijmegen Medical Centre in the Netherlands.

"This study gives attention to the diagnosis of severe pertussis, which is important because we know that there is a considerable delay in diagnosing some of these patients," said Dr. de Groot, who comoderated the session.

"It indicates that early diagnosis may offer opportunities for intervention, such as the treatment of pulmonary hypertension with drugs or exchange transfusion; however, the potential beneficial effects of these 2 interventions need to be proven in prospective studies."

Another issue that should be explored is the role of vaccination during the California outbreak, Dr. de Groot noted. "A potential increase in the number of severe cases in the United States or in California is an issue that was not mentioned in the abstract, and might raise questions about vaccination coverage in the region or the country."

Dr. Cherry and Dr. de Groot have disclosed no relevant financial relationships.

European Society for Paediatric Infectious Diseases (ESPID) 30th Annual Meeting: Abstract 31. Presented May 10, 2012.

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