Internet Queries Play Role in MRSA Surveillance

The Internet is a common source of medical information and has created novel surveillance opportunities. Vanja M. Dukic, of the University of Colorado, and colleagues, assessed the potential for Internet-based surveillance of methicillin-resistant Staphylococcus aureus (MRSA) and examined the extent to which it reflects trends in hospitalizations and news coverage. Google queries were a useful predictor of hospitalizations for methicillin-resistant S. aureus infections. Their research was published in Emerging Infectious Diseases.

As the researchers explain, Recent efforts to overcome surveillance limitations, in particular delay and limited geographic coverage, have included Internet protocol (IP) surveillance. IP surveillance monitors Internet search terms related to a specific disease, assuming that greater disease activity correlates with more searches. The best known IP surveillance is Google Flu Trends, although other researchers have created additional models. Given the lack of comprehensive surveillance, we examined whether Google search data might productively supplement existing systems to track the changing epidemiology of MRSA infections. Because MRSA, unlike influenza, is unfamiliar to many persons, we hypothesized that Internet search activity might reflect curiosity inspired by news reports and information-seeking related to actual infections or symptoms.

Dukic, et al. used the Google Trends database to obtain the proportion of all Google searches that contained the words "MRSA" or "staph." "Staph" was included because many news stories refer to MRSA as "antibiotic resistant staph." "Methicillin-resistant Staphylococcus aureus" was too infrequently searched to be useful. Google Trends reports search activity relative to the average number of similar queries in February 2004. They only included U.S. searches determined from IP addresses.

The researchers also used quarterly hospital discharge data from the University HealthSystems Consortium Clinical Database, which includes more than 90 percent of U.S. academic medical centers, to calculate the proportion of hospitalizations including an MRSA diagnosis. These data were a proxy for true MRSA incidence. They used the diagnostic code for MRSA from the International Classification of Disease, 9th Revision (V09.0). MRSA hospitalizations include CA-MRSA infections that led to hospitalization and infections that developed during a hospitalization. This database includes <99 codes per discharge, more than other national hospital discharge databases. The likelihood of recording an MRSA diagnosis increases with longer lists of codes because of the many concurrent conditions in complex hospitalizations. Some medical centers systematically used <99 diagnoses fields. They adjusted hospitalization rates for the maximum number of codes submitted by each medical center each year. Data after the 3rd quarter of 2008 were not included because of implementation of a nationwide coding change for MRSA.

As the researchers note, We report an IP surveillance model for MRSA incidence. We hypothesized that news coverage for such an unfamiliar disease would strongly influence search activity. However, news coverage did not affect the relationship between search queries and hospitalization rates before the 2007 CDC report. The congruence of the Internet search activity and the hospital discharge data suggest that their temporal pattern represents the actual trend in MRSA: an increasing incidence during 20042007, with a suggestion of seasonal variation, and no increase in 2008. This pattern is not the same pattern documented by the ABC surveillance data for invasive MRSA infections. The unfamiliarity of the public with MRSA poses a challenge to using Google Trends. Searches using the phonetic misspelling "mersa" show a parallel trend to searches using "MRSA," although they are less frequent, and the correctly spelled "methicillin" is too rare to track.

The researchers conclude, Hospitalized MRSA infections include hospital-associated MRSA infections and the more serious CA-MRSA infections. Because evidence has shown that invasive hospital-associated MRSA infections decreased during the study period, the generally upward secular trend in MRSA hospitalizations is more likely to represent the trend in CA-MRSA, especially because we now know that most MRSA infections have onset in the community. The inability to distinguish community and health care infections is nonetheless a limitation of the Google and the hospitalization data. Although some hospital databases include more hospitals, they include fewer diagnostic codes. Therefore, there are no additional comprehensive data available for MRSA incidence. The lack of any true standard for MRSA incidence is why IP surveillance is potentially useful.

Reference: Dukic VM, David MZ, Lauderdale DS. Internet queries and methicillin-resistant Staphylococcus aureus surveillance. Emerg Infect Dis. June 2011.

Figure 1. Weekly counts of news coverage (newspaper stories, wire service stories, and television and radio news transcripts) that mention "MRSA" (methicillin-resistant Staphylococcus aureus) or "staph," 20042008. Extracted from the LexisNexis Academic Database.

Figure 2. Actual and predicted hospitalization rates per 1,000 hospitalizations with an International Classification of Disease, 10th Revision, diagnostic code for methicillin-resistant Staphylococcus aureus (MRSA) and the fraction of Google search queries for "MRSA" or "Staph" (relative to the fraction of February 2004), 20042008.




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