People who have their tonsils or adenoids removed before age 9 years are at higher risk for respiratory, infectious, and allergic diseases up to the age of 30 years, a population-based study of almost 1.2 million patients suggests.

"We found that tonsillectomy was associated with a nearly tripled risk of upper respiratory tract diseases, and that adenoidectomy was associated with doubled risk of [chronic obstructive pulmonary disease] and upper respiratory tract diseases and nearly doubled risk of conjunctivitis," Sean Byars, PhD, from the University of Melbourne in Victoria, Australia, and colleagues write.

"Understanding the longer-term impact of these surgeries is critical because the adenoids and tonsils are parts of the immune system, have known roles in pathogen detection and defense, and are usually removed at ages when the development of the immune system is sensitive," said Byars.

Byars and colleagues say the findings should prompt renewed efforts to identify nonsurgical alternatives for treatment. However, at least one expert says the results should be interpreted with caution because of the study design and because the underlying cause for the original surgery can have negative effects of its own.

Byars and colleagues analyzed data from the Danish Birth Registry, which included 1,189,061 individuals for health outcomes through age 30 years. Participants included in the analysis were born between 1979 and 1999 and were followed until 2009.

Some 17,460 participants had had their adenoids removed, 11,830 had had their tonsils removed, and 31,377 underwent an adenotonsillectomy. The remaining participants in the sample served as controls.

When the investigators calculated the long-term risks of 28 different diseases among each group, they found that tonsillectomy was associated with nearly a threefold relative risk (RR) of diseases of the upper respiratory tract (RR, 2.72; 95% confidence interval [CI], 1.54 – 4.80) compared with children who had not had their tonsils removed.

This translated into a number needed to treat (NNT) of only 5, "suggesting that only about 5 tonsillectomies would need to be performed for an additional upper respiratory tract disease to be associated with one of those patients," the authors explain.

Adenoidectomy, in turn, was associated with a greater than twofold risk for chronic obstructive pulmonary disease (RR, 2.11; 95% CI, 1.53 – 2.92) and a nearly twofold increase for respiratory tract diseases (RR, 1.99; 95% CI, 1.51 – 2.63) and conjunctivitis (RR, 1.75; 95% CI, 1.35 – 2.26).

"For some diseases, even modest increases in relative risk (RR, 1.17-1.65) resulted in relatively large increases in absolute risk (2%-9%) and low NNTs (NNT-harm <50) because of the high prevalence of these diseases in the population," the researchers explain.

Best Available Evidence

Richard Rosenfeld, MD, distinguished professor of otolaryngology at SUNY Downstate Medical Center in Brooklyn, New York, acknowledged that evidence-based medicine means making clinical decisions using the best evidence available. Often, the "best" evidence is an observational study.

"These biases could distort the findings both in terms of magnitude and significance," Rosenfeld told, "and we cannot simply ignore these. We must view the results as provocative, not definitive."