Murine typhus is a common zoonotic disease in endemic foci of southern Texas, where a mean of 48 cases were reported annually from 1990 through 2006 (15
). However, before this investigation, murine typhus was not believed to occur commonly in the Austin/Travis County area, and only 2 cases were identified before 2007. This investigation identified 33 patients with laboratory-confirmed cases, nearly 70% of whom were hospitalized from March through November 2008. In addition, 2 murine typhus cases reported in Austin in September 2007 likely represent some of the first cases associated with this emergent focus. These findings represents the first large-scale outbreak reported in Austin/Travis County since eradication efforts were coordinated in this part of Texas in the 1940s (TDSHS, unpub. data).
The clinical features and age distribution of case-patients reported here are similar to those found in case-patients reported in other murine typhus studies (4
). Although 70% of the case-patients identified during this outbreak were hospitalized, this percentage is slightly less than what was observed by Taylor et al. (16
) during a study of 200 cases in Texas from 1980 through 1984, in which 85% of patients were hospitalized and 1% died. Though no deaths were reported during this 2008 outbreak, nearly one third of all patients were admitted to the intensive care unit with complications (including pneumonia, coagulopathy, and renal failure) that demonstrated the severity of illness.
Delaying treatment for murine typhus increases the duration of symptoms and risk for complications (4,17
). Treatment should always be initiated on the basis of clinical and epidemiologic considerations alone without waiting for a laboratory confirmation of the diagnosis. In this outbreak, 48% of patients did not receive treatment with doxycycline, the drug of choice for treatment for rickettsial diseases. The lack of doxycycline administration and the reported lag time of 1 week to nearly 3 weeks between symptom onset and antimicrobial drug treatment experienced by most patients may have been associated with a delay in recognizing that the cases were murine typhus, because of the perception that the disease was not present in Austin. Despite this finding, the difference in hospitalization and complication rates did not appear to be significant between patients with and without proper antimicrobial drug treatment. However, the small sample size may have precluded a robust comparison of these data.
Strong serologic evidence of exposure to rickettsiae was detected among opossum and domestic animal populations in Austin/Travis County. More than one third of all animals tested were seropositive with R. typhi
antigen. Of particular interest, >70% of opossums tested were seropositive with R. typhi
antigen. Further studies are needed to determine the specific role that opossums play in the ecology of murine typhus in the Austin area. Exposure to other rickettsiae in the spotted fever group also cannot be excluded, particularly for R. felis
, which is very common in cat fleas obtained from opossums (7,12
). The serologic findings observed here are similar to what has been observed in studies of disease-endemic regions in southern Texas and California, USA, where opossums are hosts for fleas containing R. typhi
and R. felis
). In Los Angeles, California, and Corpus Christi, Texas, 42% and 25% of opossums were found to be seropositive for R. typhi
, respectively, although seropositive rats were rarely or never detected (7,9
). These studies have resulted in a reevaluation of the classic urban cycle of murine typhus in suburban disease-endemic areas in the continental United States, where opossums, domestic cats, and cat fleas—and not rodents and their fleas—are considered to be a primary source of infection (2
Although none of the rats in this study were seropositive for R. typhi
, the small sample size tested (n = 4) limits our ability to draw conclusions regarding the contribution of rats and their arthropods to the dynamics of murine typhus in this area. Additionally, presumptions regarding contributions of various animal species are limited because only serologic findings were positive; active infection with either R. typhi
or R. felis
was not detected in any of the samples tested. While none of the fleas were positive for either R. typhi
or R. felis
DNA, this result is not entirely unexpected considering the infrequency with which positive fleas were detected in similar studies. For instance, Boostrom et al. (7
) identified only 3 R. typhi
and 11 R. felis
positive fleas out of a sample of 529 from highly endemic parts of southern Texas. Still, R. feli
s may be circulating within this area because both pathogens appear to be maintained in complex ecologic cycles (2,7
). More specific studies targeting larger numbers of statistically representative domestic animals and wildlife are needed to better discern complicated human-animal-disease dynamics.
Murine typhus may now be established in the Austin/Travis County area and should be considered an ongoing public health threat. Although, the idea that persons have been infected with R. felis
(which has been previously found to infect a patient in Texas) cannot be totally excluded (8
). Continued public health education efforts are needed in the Austin/Travis County area regarding the emergence of flea-borne rickettsiosis and the likely risk factors for infection, with an emphasis on avoiding contact with wild animals and controlling fleas on pets and around the home with approved products. Physicians in the area should maintain an increased vigilance in detecting and diagnosing suspected murine typhus cases as well as other rickettsioses, because timely treatment with the appropriate antimicrobial drug therapy is critical for limiting severe outcomes.