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Cat scratch disease in US primarily affects South, children
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People living in the southern United States and children aged 5 to 9 years are at greatest risk for contracting cat scratch disease, according to a retrospective analysis of all nationally diagnosed cases of the infection from 2005 to 2013.
Cat scratch disease (CSD) is caused by Bartonella henselae, a bacterium spread among cats by the cat flea and transmitted to humans by cat scratches and occasionally cat bites. While often benign, the infection can be severe, especially in patients with immunocompromising conditions such as AIDS. Researchers from the CDC aimed to gain more information about the epidemiology and extent of CSD in the U.S. in order to direct prevention efforts to those at greatest risk.
Christina A. Nelson
“The epidemiology of CSD may have changed in the past few decades because of improved diagnostic tests for CSD and other conditions that mimic CSD,” Christina A. Nelson, MD, MPH, epidemiologist in the Bacterial Diseases Branch of the CDC’s Division of Vector-Borne Diseases, and colleagues wrote. “Improved understanding of CSD may facilitate recognition by clinicians and identification of risk groups for whom education about cats and flea control is particularly helpful.”
Nelson and colleagues analyzed Truven Health MarketScan Commercial Claims and Encounters database records from 2005 to 2013. They identified all insurance claims records for patients aged younger than 65 years with an inpatient or outpatient visit that included the ICD-9 code for CSD (078.3).
During the study period, 13,273 patients were diagnosed with CSD: 12,735 outpatients and 538 inpatients. The average annual incidence of CSD was 4.5 outpatient diagnoses per 100,000 population (range, 4-5.7 per 100,000) and 0.19 inpatient admissions per 100,000 population (range, 0.17-0.22 per 100,000).
According to the investigators, the incidence was greatest in the West South Central, East South Central and South Atlantic regions (6.1-6.4 cases per 100,000 population), with 26.3% of all cases occurring in the South Atlantic region. The incidence was lowest in the Mountain region (2.1 cases per 100,000 population), where cat fleas are less common because of the dry climate. The highest incidence of disease was among children aged 5 to 9 years (9.4 cases per 100,000 population). Children aged 14 years and younger accounted for 32.5% of total diagnoses. Compared with outpatients, inpatients were more likely to be male, aged 50 to 64 years and reside in the South, the researchers said.
Researchers attributed a recent decline in U.S. cases of cat scratch disease (CSD) to improved flea control methods and products and better diagnostics that can distinguish between CSD and similar diseases.
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To assess changes in the epidemiology of CSD during this time period, Nelson and colleagues divided the data into two, 3-year periods (2005-2007 and 2011-2013). The incidence of patients given a CSD diagnosis decreased from 5.5 cases per 100,000 population in the early period to 4.4 cases per 100,000 population in the later period.
The researchers hypothesized that the reduced incidence in cases may be partly attributable to improved flea control methods and products that may have reduced the risk for B. henselae transmission to humans. Additionally, improved diagnostics for other causes of lymphadenopathy may have prevented overdiagnosis of CSD in recent years.
They estimated that the annual total cost of CSD among people aged younger than 65 years is $2,928,000 for outpatients and $6,832,000 for inpatients, totaling $9,760,000 annually in direct medical costs for CSD.
“CSD causes a substantial burden of disease nationwide and disproportionately affects children,” the researchers wrote. “Educational efforts should focus on cat owners, particularly those with children in the household or those with immunocompromising conditions.” – by Sarah Kennedy
Disclosure: The researchers report no relevant financial disclosures.
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