The following are pre-publication drafts of articles from the Morbidity and Mortality Weekly Report dated August 11, 1995. Late-breaking articles, and final editorial revisions are not included; therefore, these articles should be considered preliminary, and not to be released to the public. --CDC -------------------------------------------------------------- Heat-Related Mortality -- Chicago, July 1995 During July 12-16, 1995, Chicago experienced unusually high maximum daily temperatures, ranging from 93 F to 104 F (33.9 C to 40.0 C). On July 13, the heat index* peaked at 119 F (48.3 C)--a record high for the city. This report describes the heat- related deaths reported by the Cook County Medical Examiner's Office (CCMEO) during this heat wave. Deaths classified as heat-related by the CCMEO met one of the following three criteria: 1) core body temperature of the decedent greater than or equal to 105 F ( greater than or equal to 40.6 C) at the time of or immediately after death, 2) substantial environmental or circumstantial evidence of heat as a contributor to death (e.g., decedent found in a room without air conditioning, all windows closed, and a high ambient temperature), or 3) decedent in a decomposed condition without evidence of other cause of death and with evidence that the decedent was last seen alive during the heat wave period. During July 11-27, a total of 465 deaths were certified as heat-related by the CCMEO (Figure 1); during July 4-10, no deaths were certified as heat-related. The highest number of heat-related deaths previously certified by the CCMEO--associated with a heat wave in 1988--was 77. The number of heat-related deaths peaked 2 days after the heat index peaked. Deaths increased from 49 (July 14) to a maximum of 162 (July 15) (Figure 1). Of the 465 decedents, 257 (55%) were male. Based on race-specific data, 229 (49%) decedents were black; 215 (46%), white; and 21 (5%), other racial/ethnic groups.** Within racial categories, 128 (56%) blacks were male, and 114 (53%) whites were male. Of the 437 decedents for whom age could be determined, age ranged from 3 years to 103 years (median: 75 years, mean: 72 years); 222 (51%) were aged greater than or equal to 75 years. During July 13-21 (when most heat-related deaths were certified by the CCMEO), a total of 1177 deaths occurred in Chicago--an 85% increase over the same period in 1994 (637 deaths). Reported by: ER Donoghue, MD, MB Kalelkar, MD, MA Boehmer, Office of the Medical Examiner County of Cook, Chicago; J Wilhelm, MD, S Whitman, PhD, G Good, MS, S Lyne, RSM, Commissioner, City of Chicago Dept of Health; J Lumpkin, MD, L Landrum, MUPP, BJ Francis, MD, State Epidemiologist, Illinois Dept of Public Health. Div of Environmental Hazards and Health Effects, National Center for Environmental Health, CDC. Editorial Note: Excess mortality from hyperthermia and cardiovascular disease during heat waves has been well documented (2,3). The findings in Chicago by the CCMEO that blacks, males, and the elderly appear to be particularly susceptible to heat-related death are similar to previous studies of heat waves. During public health crises such as heat waves, state-specific mortality data are often incomplete or unavailable; therefore, data from medical examiners' (MEs') offices may be used to assess mortality during such crises. Although ME-based surveillance for heat-related deaths can prompt timely public health responses during heat waves, use of ME data is limited because of selection bias. Individual MEs and other persons who certify deaths (e.g., coroners and attending physicians) use varying criteria to determine which deaths are heat-related, largely because no standardized definition exists. In the United States, lack of a uniform definition for heat-related death results in substantial variation in the criteria used to certify such deaths. The most stringent definition of heat-related death is a core body temperature of greater than or equal to 105 F (greater than or equal to 40.6 C) taken at the time of death, with no other reasonable explanation of death. This definition precludes certifying any death as heat-related if core body temperature is not measured before or near the time of death and may underestimate excess heat-related mortality. A nonspecific definition of heat-related death (which could include all deaths that occur during a heat wave) would overestimate this mortality. The definition used by the CCMEO to classify deaths as heat-related has remained unchanged since 1978 and is based on a reasonable approach (i.e., evidence of exposure to high levels of environmental heat). These two factors (as well as the finding that the data about heat-related deaths are consistent with preliminary data about total mortality in Chicago during July 1995) suggest that the CCMEO data did not overestimate heat-related mortality during that period. The differential impact of a heat wave on specific population subgroups cannot be determined based on ME data alone because of incompleteness and potential bias (3,4). For example, based on CCMEO data, a disproportionately high number of heat-related deaths occurred among blacks in Chicago on July 15 (Figure 1). Because CCMEO data do not include all deaths nor equally represent all socioeconomic status (SES) categories, it is not yet possible to completely describe mortality, calculate death rates, or determine whether the race- and sex-specific distribution of the heat-related deaths is disproportionate to overall mortality in Chicago. A case-control study is under way in Chicago to examine the influences of SES and specific environmental factors on heat-related mortality. Despite their limitations, the data in this report confirm that 1) public health information should be directed toward susceptible populations (e.g., the elderly), 2) as in other heat waves (2,3), the time between the beginning of a heat wave and the resulting heat-related deaths (e.g., 2 days in Chicago) should be sufficient to disseminate prevention messages to the public, and 3) a standardized definition of heat-related death is needed. Heat-related mortality is preventable. The most effective measures for preventing heat-related illness and death include reducing physical activity, drinking additional nonalcoholic liquids, and increasing the amount of time spent in air-conditioned environments. In addition, because increased air movement (e.g., fans) has been associated with heat stress when the ambient temperature exceeds approximately 100 F (37.8 C) and because fans are not protective at temperatures greater than 90 F (greater than 32.3 C) with humidity greater than 35% (the exact temperature varies with the humidity), fans should not be used for preventing heat-related illness in areas with high humidity (3,5). To further define information that can be used to identify persons at greatest risk during hot weather, CDC is collaborating with Chicago and Illinois health officials to determine risk factors to better target persons at increased risk for heat-related illness or death. A standard definition for heat-related death will be addressed at the February 1996 meeting of the American Academy of Forensic Sciences. References 1. Rothfusz LP. The heat index "equation" (or, more than you ever wanted to know about heat index). Fort Worth, Texas: National Oceanic and Atmospheric Administration, National Weather Service, Office of Meteorology, 1990; publication no. SR 90-23. 2. Wainwright S, Buchanan S, Mainzer H. Cardiovascular mortality: the hidden peril of heat waves [Abstract]. In: Program and abstracts of the CDC Epidemic Intelligence Service 43rd annual conference. Atlanta, Georgia: US Department of Health and Human Services, Public Health Service, CDC, 1994. 3. Kilbourne EM, Choi K, Jones TS, Thacker SB, and the Field Investigation Team. Risk factors for heat stroke: a case control study. JAMA 1982;247:3332-6. 4. Jones TS, Liang AP, Kilbourne EM, et al. Morbidity and mortality associated with the July 1980 heat wave in St. Louis and Kansas City, Missouri. JAMA 1982;247:3327-31. 5. Lee DH. Seventy-five years of searching for a heat index. Environ Res 1980;22:331-56. * The heat index (i.e., the apparent temperature) is an estimation of the influence of temperature and humidity on the evaporative and radiative transfer of heat between a typical human and the atmosphere. The values can be derived from a chart available through the National Weather Service (1). ** The CCMEO categorizes race of decedents as black, white, or other. Translocation of Coyote Rabies -- Florida, 1994 Translocation of a rabies variant from one area to another has been identified increasingly in the United States. During November and December 1994, rabies was diagnosed in five dogs from two associated kennels in Florida; in addition, two other dogs being kept at one of the kennels died with suspected, but unconfirmed, rabies. Rabies virus recovered from the five dogs was identified as a variant not previously found in Florida but endemic in coyotes (Canis latrans) in south Texas. The suspected source of infection was translocation of infected coyotes from Texas to Florida. This report summarizes the findings of an investigation of these cases by the Alachua County Public Health Unit, the Florida Department of Health and Rehabilitative Services, and CDC. On November 21, 1994, a Walker hound used for fox hunting escaped from one of the fenced kennels; on recapture later that day, the dog was unusually aggressive and bit one of the kennel owners. The dog was euthanized and tested positive for rabies. On November 21, the Alachua County Public Health Unit identified 102 dogs and 10 cats potentially exposed to this dog while it was loose and established a 20-square-mile quarantine area. Measures implemented by public health and animal-control authorities included vaccinating against rabies all unvaccinated dogs and cats within the quarantine area and administering booster vaccine to previously vaccinated animals, prohibiting movement of animals in and out of the quarantine area, systematically mailing rabies update advisories to residents of the quarantine area, and--with the assistance of the news media--increasing rabies surveillance by requesting reports of persons or animals that had been bitten by an animal. As a result of exposure to this dog or other animals in the quarantine area, 26 persons received rabies postexposure treatment, and three persons received preexposure prophylaxis. Concurrent investigations by the Alachua County Public Health Unit revealed that two other dogs from the same kennel had died on November 10 and November 18. Neither of these dogs were tested for rabies; however, rabies was suspected and confirmed in four additional dogs (three from the same kennel and one from an associated kennel), who died November 28 (one), November 30 (one), and December 1 (two). Rabies in the five dogs tested was confirmed at CDC, and the isolates were identified as the variant associated with coyotes in south Texas (1). None of the seven dogs with presumed or confirmed rabies had a history of rabies vaccination. All seven dogs had been kept in Florida for greater than or equal to 7 months preceding their deaths. Several times each week during September and October, the kennel owner, family members, and a business associate hunted coyotes that were kept in a 320-acre fenced foxpen 18 miles from the dog kennels. The foxpen had not been rented for use by other hunters. The foxpen had housed 20-25 coyotes, which were reported to have been captured in Florida during February 1994 and placed in the pen during the same month with gray foxes and raccoons. The coyotes were reported to have been fed regularly, and no ill or dead wildlife had been noted in the enclosure within the previous 6 months. Six of the dogs with presumed or confirmed rabies had accompanied the hunters in the foxpen. The one rabid dog that was never taken to the foxpen had shared a kennel with two of the dogs with rabies. Four of the seven rabid dogs also had been to a field trial with approximately 400 other hunting dogs in late October; none of these other dogs are known to have died from rabies. Depopulation of the free-ranging carnivores within the enclosed foxpen was instituted with the assistance of the Florida Game and Fresh Water Fish Commission because the affected dogs in the foxpen may have been exposed to other rabid animals. The potentially exposed or infected animals included 32 coyotes, five raccoons, two gray foxes, two bobcats and one cat; diagnostic tests of these animals at CDC were negative for rabies. Continuing surveillance in the quarantine area subsequently identified rabies in a puppy that had been bitten by the escaped rabid dog. Reported by: T Belcuore, MS, Alachua County Public Health Unit; L Conti, DVM, G Hlady, MD, L Crockett, MD, R Hopkins, MD, State Epidemiologist, Florida Dept of Health and Rehabilitative Svcs. M Dunbar, DVM, Florida Game and Fresh Water Fish Commission. Viral and Rickettsial Zoonoses Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases, CDC. Editorial Note: The episode described in this report resulted in six confirmed and two presumed cases of dog rabies and the need for rabies postexposure treatment of 26 persons. It highlights the increasing problem of animal rabies in the United States, which reached record levels in 1993. The incubation period for rabies in the cases in this report and the rabies variant with which they were infected suggest that the source of infection was coyotes in the foxpen during October. Although the incubation period for rabies in dogs usually is 3-8 weeks, it can vary from 10 days to 8 1/2 months (2). The rabies variant identified is not present in animal populations of the southeastern United States but is found exclusively in 17 counties in southern Texas. Because the dogs had not traveled outside Florida, translocation of infected animals from Texas is suspected. A similar case of dog rabies in Alabama was attributed to coyotes transported for hunting purposes from Texas to Alabama (3). Enzootic dog rabies has been nearly eliminated in the United States as the result of effective mass vaccination programs and programs initiated during the 1950s to control stray animal populations. Dog-to-dog transmission of the magnitude described in this report has not been documented since the early 1970s, except in areas along the U.S.-Mexico border. However, 12 of the 25 human rabies cases diagnosed in the United States since 1980 were associated with exposure to dog rabies viruses outside the United States or near the U.S.-Mexico border. In the cases in this report, rabies transmission to the dogs probably could have been prevented if the dogs had been appropriately vaccinated against rabies. Since 1988, rabies in coyotes in southern Texas has accounted for most coyote-associated rabies in the United States, including 70 of 75 cases in 1992, and 71 of 74 cases in 1993 (3). The coyote rabies epizootic has been a source for infection for unvaccinated domesticated dogs and further expansion of rabies. Since 1991, at least two human deaths have been associated directly with the southern Texas rabies variant (4,5), probably associated with interactions between coyotes and dogs. In addition to established measures for preventing rabies, including mandatory vaccination of domesticated dogs (6) and prompt postexposure treatment of humans (7), the development of safe and effective oral rabies vaccines for coyotes and other wild carnivores would be a potentially important adjunct control strategy. The interstate transport of wildlife from geographic areas with enzootic hazards to new areas has resulted in disease outbreaks with substantial public health and economic impact. For example, the current raccoon rabies epizootic in the mid-Atlantic and northeastern United States is the direct consequence of translocation and spread of infected raccoons from the southeastern United States during the late 1970s; raccoons are now the primary rabies reservoir in the United States (3). A recent surge in popularity of coyote hunting in the southeastern United States has resulted in an increase in sales of wild canids for foxpens; although coyotes are indigenous to that region, some of these animals may have been imported illegally. Intensified surveillance for this rabies variant is warranted in those states where residents participate in coyote hunting in enclosures. In addition to rabies, public health risks associated with wildlife translocation include zoonotic infections such as plague, hantavirus pulmonary syndrome, brucellosis, echinococcosis, Lyme disease, Rocky Mountain spotted fever, ehrlichiosis, and tularemia. However, federal and state regulations have not been applied consistently to the interstate movement of native wildlife. Because of the public health risks and lack of feasible methods to certify animals as free of many of these zoonotic agents, restrictions on the interstate movement of native wildlife may need to be considered. The Florida Department of Health and Rehabilitative Services and CDC are strain-typing all rabies variants found in wild and domestic canids. No additional isolates of the coyote rabies variant have been identified in Florida. References 1. Clark K, Neill SU, Smith JS, et al. Epizootic canine rabies transmitted by coyotes in south Texas. J Am Vet Med Assoc 1994;204:536-40. 2. Tierkel ES. Canine rabies. In: Baer GM, ed. The natural history of rabies. New York: Academic Press, 1975:123-37. 3. Krebs JW, Strine TW, Smith JS, Rupprecht CE, Childs JE. Rabies surveillance in the United States during 1993. J Am Vet Med Assoc 1994;205:1695-709. 4. CDC. Human rabies--Texas, Arkansas, and Georgia, 1991. MMWR 1991;40:765-9. 5. CDC. Human rabies--Alabama, Tennessee, and Texas, 1994. MMWR 1995;44:269-72. 6. CDC. Compendium of animal rabies control, 1995: National Association of State Public Health Veterinarians, Inc. MMWR 1995;44(no. RR-2). 7. ACIP. Rabies prevention--United States, 1991: recommendations of the Immunization Practices Advisory Committee (ACIP). MMWR 1991;40(no. RR-3). Laboratory Practices for Diagnosis of Tuberculosis -- United States, 1994 The increase in cases of tuberculosis (TB) during 1985-1992 and the emergence of multidrug-resistant Mycobacterium tuberculosis strains led to recommendations for rapid laboratory testing to support control efforts and selection of proper therapy (1,2). Many laboratories have adopted the recommendations to use rapid acid-fast bacilli (AFB) smears, growth detection (i.e., primary culture), identification, and drug-susceptibility testing for M. tuberculosis (3). The regulations implementing the 1988 Clinical Laboratory Improvement Amendments* (CLIA) require all laboratories that perform any mycobacteriology testing to enroll in federally approved proficiency testing (PT) programs. This report summarizes information reported by the laboratories to PT programs in the United States about their practices for M. tuberculosis. The PT programs submit samples of unknown content to laboratories for testing in the same manner as actual patient specimens; the laboratories subsequently report methods and test results to the program. In 1994, the U.S. Department of Health and Human Services approved six PT programs for mycobacteriology testing: five programs (the College of American Pathologists [CAP]; the states of New Jersey, New York, and Wisconsin; and the Commonwealth of Puerto Rico) provide PT testing for AFB smears, growth detection, organism identification, and drug-susceptibility testing; and one program (the American Association of Bioanalysts) provides testing for AFB smears only. To determine the number of laboratories that performed various levels of testing for M. tuberculosis, laboratories were classified into four categories based on the practices specifically reported for M. tuberculosis. These categories were laboratories that perform 1) AFB smears and refer all specimens for primary culture to another laboratory; 2) AFB smears and primary cultures for M. tuberculosis but refer all AFB-positive culture isolates for organism identification and drug-susceptibility tests; 3) AFB smears and primary culture with identification of M. tuberculosis isolates but refer isolates for drug-susceptibility testing; and 4) AFB smears, primary culture, identification, and drug-susceptibility testing for M. tuberculosis. Some laboratories must enroll in more than one PT program to meet the requirements of both state laboratory licensure programs and private laboratory accreditation programs. Therefore, because most laboratories were enrolled in the CAP PT program, the actual number of laboratories in each of the four categories ranges from a minimum that represents the enrollment of CAP only to a maximum that represents the total reported enrollment for all PT programs. In 1994, a total of 2862 mycobacteriology laboratories were enrolled in PT programs; 2459 (85%) were enrolled in CAP. Category-specific enrollment ranged from 506 (CAP only) to 683 (all PT programs) for laboratories that perform AFB smears only, 1126-1166 for those that perform primary culture without organism identification, 568-699 for those that perform primary culture and identification, and 259-314 for those that perform primary culture, identification, and drug-susceptibility testing (Figure 1). Of the 2862 mycobacteriology laboratories, 2179 reported performing primary culture for M. tuberculosis. Of these, 1166 (54%) referred any AFB-positive isolates to another laboratory for organism identification and drug-susceptibility testing, 699 (32%) performed primary culture with identification, and 314 (14%) performed primary culture, identification, and drug-susceptibility testing. Similarly, of the 1953 laboratories enrolled in CAP only that reported performing primary culture for M. tuberculosis, 1126 (58%) referred any AFB-positive isolates to another laboratory for organism identification and drug-susceptibility testing, 568 (29%) performed primary culture with identification, and 259 (13%) performed primary culture, identification, and drug-susceptibility testing. Reported by: N Serafy, American Association of Bioanalysts, Brownsville, Texas. N Kubala, G Woods, MD, College of American Pathologists, Northfield, Illinois. M Salfinger, MD, I Salkin, PhD, New York State Dept of Health. R La Fisca, New Jersey Dept of Health. C Robles Rivera, Puerto Rico Dept of Health. N Bourdeau, Univ of Wisconsin Center for Health Sciences, Madison. Div of Laboratory Systems, Public Health Practice Program Office, CDC. Editorial Note: Rapid laboratory testing to identify and determine the drug susceptibility of M. tuberculosis isolates is vital to effective diagnosis, treatment, and control of TB in the community. The findings in this report indicate that for a substantial proportion of TB cases, organism identification and drug-susceptibility determinations may be delayed because at least 54% of laboratories performing primary cultures for M. tuberculosis must refer AFB culture isolates to another laboratory for complete analysis. Although both solid and liquid media together are recommended for culturing M. tuberculosis, the liquid-culture method is needed to rapidly isolate and detect the organism in primary culture and to test susceptibility to the primary anti-TB drugs (1). In addition to decreasing the time required to detect and isolate mycobacteria, liquid-culture methods also increase the sensitivity of culture for M. tuberculosis (1,4). Although primary culture-isolation methods are not routinely reported to PT programs, a 1992 survey of 749 laboratories that performed primary culture with referral of all isolates to another laboratory indicated that 97 (13%) were using the recommended liquid-culture method (CAP, unpublished data, 1994). In addition, a survey of hospital laboratories in 1992 indicated that only 35 (14%) of 248 laboratories that referred isolates for identification of M. tuberculosis used the recommended liquid-culture method compared with 139 (50%) of 280 laboratories that routinely identified isolates of M. tuberculosis (CDC, unpublished data, 1994). Reasons for the continued use of solid-culture medium alone may reflect minimum test-volume requirements and higher costs associated with the liquid-culture system. The exclusive use of solid-medium culture methods delays isolation of M. tuberculosis by an average of 7-10 days (4), thereby delaying organism identification to confirm diagnosis. In addition, the referral of AFB-positive culture growth to another laboratory may result in delays associated with transport. These delays also may prolong determination of whether isolates are resistant to anti-TB drugs: in 1994, based on test results for 28 states, 8% of cases were resistant to isoniazid (INH) and 2% were resistant to both INH and rifampin (5). At least one state (i.e., New York) has regulations that prohibit laboratories from performing primary culture if the laboratory does not perform identification of M. tuberculosis. The findings in this report are subject to at least two limitations. First, data were unavailable about the proportion of all M. tuberculosis specimens tested by each of the four categories of laboratories enrolled in PT programs. Second, data were unavailable to determine whether laboratories that refer culture isolates for identification have adopted use of liquid-culture methods. Laboratories should select culture tests that provide rapid identification of M. tuberculosis and drug-susceptibility test results to enable early confirmation of the diagnosis and initiation of infection-control measures and case-finding. Laboratories that perform only primary culture for M. tuberculosis should determine whether referral of the patient specimen, rather than culture isolates, may decrease the time required for identification and drug-susceptibility testing. References 1. Tenover FC, Crawford JT, Huebner RE, Geiter LJ, Horsburgh CR Jr, Good RC. The resurgence of tuberculosis: is your laboratory ready? J Clin Microbiol 1993;31:767-70. 2. CDC. National action plan to combat multidrug-resistant tuberculosis. MMWR 1992;41(no. RR-11). 3. Woods G, Witebsky F. Mycobacterial testing in clinical laboratories that participate in the College of American Pathologists Mycobacteriology E survey: results of a 1993 questionnaire. J Clin Microbiol 1995;33:407-12. 4. Nolte FS, Metchock B. Mycobacterium. In: Murray PR, Baron EJ, Pfaller MA, Tenover FC, Yolken RH, eds. Manual of clinical microbiology. 6th ed. Washington, DC: American Society for Microbiology, 1995:400-37. 5. CDC. Tuberculosis morbidity--United States, 1994. MMWR 1995;44:387-9,395. * 42 CFR 493.825. Notice to Readers Recommendations for Test Performance and Interpretation from the Second National Conference on Serologic Diagnosis of Lyme Disease The Association of State and Territorial Public Health Laboratory Directors, CDC, the Food and Drug Administration, the National Institutes of Health, the Council of State and Territorial Epidemiologists, and the National Committee for Clinical Laboratory Standards cosponsored the Second National Conference on Serologic Diagnosis of Lyme Disease held October 27-29, 1994. Conference recommendations were grouped into four categories: 1) serologic test performance and interpretation, 2) quality-assurance practices, 3) new test evaluation and clearance, and 4) communication of developments in Lyme disease (LD) testing. This report presents recommendations for serologic test performance and interpretation, which included substantial changes in the recommended tests and their interpretation for the serodiagnosis of LD. A two-test approach for active disease and for previous infection using a sensitive enzyme immunoassay (EIA) or immunofluorescent assay (IFA) followed by a Western immunoblot was the algorithm of choice. All specimens positive or equivocal by a sensitive EIA or IFA should be tested by a standardized Western immunoblot. Specimens negative by a sensitive EIA or IFA need not be tested further. When Western immunoblot is used during the first 4 weeks of disease onset (early LD), both immuno- globulin M (IgM) and immunoglobulin G (IgG) procedures should be performed. A positive IgM test result alone is not recommended for use in determining active disease in persons with illness greater than 1 month's duration because the likelihood of a false-positive test result for a current infection is high for these persons. If a patient with suspected early LD has a negative serology, serologic evidence of infection is best obtained by testing of paired acute- and convalescent-phase serum samples. Serum samples from persons with disseminated or late-stage LD almost always have a strong IgG response to Borrelia burgdorferi antigens. It was recommended that an IgM immunoblot be considered positive if two of the following three bands are present: 24 kDa (OspC)*, 39 kDa (BmpA), and 41 kDa (Fla) (1). It was further recommended that an that IgG immunoblot be considered positive if five of the following 10 bands are present: 18 kDa, 21 kDa (OspC)*, 28 kDa, 30 kDa, 39 kDa (BmpA), 41 kDa (Fla), 45 kDa, 58 kDa (not GroEL), 66 kDa, and 93 kDa (2). The details of both plenary sessions and the work group deliberations are included in the publication of the proceedings, which is available from the Association of State and Territorial Public Health Laboratory Directors; telephone (202) 822-5227. References 1. Engstrom SM, Shoop E, Johnson RC. Immunoblot interpretation criteria for serodiagnosis of early Lyme disease. J Clin Microbiol 1995;33:419-22. 2. Dressler F, Whelan JA, Reinhart BN, Steere AC. Western blotting in the serodiagnosis of Lyme disease. J Infect Dis 1993;167:392-400. * The apparent molecular mass of OspC is dependent on the strain of B. burgdorferi being tested. The 24 kDa and 21 kDa proteins referred to are the same.