Recent data suggest that tuberculosis in the United
States is a seasonal disease and latitude-dependant factors do not appear to be
associated with the peak in the spring and a decreased incidence in late fall.
Children aged younger than 5 years had the greatest
seasonal amplitude of 55.5%. In addition, cases associated with disease
clusters also had a significant seasonal amplitude of 44.9%.
Researchers from the CDC conducted a time series
decomposition analysis of TB cases reported to the CDC between 1993 and 2008.
They calculated the seasonal amplitude of TB for the population as a whole and
for populations with select demographic, clinical and epidemiologic
During the 16-year period, there were 243,432
laboratory-confirmed TB cases. The seasonal amplitude for the United States was
21.4% there were 21.4% more cases of TB diagnosed during the peak month
than in the trough month.
The greatest number of cases decreased between March and
May in 15 of the 16 years. The month with the least number of cases was
November or December for all 16 years. The peak month was March and the trough
month was November.
The data suggest that in the United States,
latitude-dependent factors, including reduced winter sunlight exposure and its
potential effects on vitamin D levels, may not contribute significantly to
seasonality, the researchers concluded. Increased seasonality among
children and cases clustered by genotype may be due to increased transmission
in winter with progression to disease diagnosed in spring.
Willis MD. Clin Infect Dis. 2012;54:1553-1560.
The researchers report no relevant financial