A 53-year-old woman went hiking in the foothills of Mount Hamilton in Santa Clara County on September 1, 2001, where she swam in a muddy pond. Eleven days later, she had the onset of shaking chills, fever of 38.9 C myalgias, ankle and wrist pain, and headache. Her fever resolved, but 4 days later nausea, vomiting, diarrhea, and a worsening headache developed and she went to urgent care. Initial laboratory test results including cerebrospinal fluid, blood urea nitrogen, and creatinine were normal, and she was treated for gastroenteritis with promethazine HC1 and fluids.
Three days later, oliguria developed. On September 19, she was admitted with oliguric renal failure and signs including an erythematous macular rash on her face and pretibial macular blanching lesions on her legs. Over the next few days, a persistent cough with rales developed, and peak levels of blood urea nitrogen were 101 and creatinine were 9.5. Urinalysis showed 1+ blood, 6-10 erythrocytes, 0-3 leukocytes, and 3+ protein. Though her leukocytes were normal at 5.9 k/muL with 84% polymorphonuclear leukocytes (PMNs), her platelet count was low at 122,000. Mild transaminasemia also developed as well as an elevated International Normalized Ratio (INR). She was treated with high-dose penicillin G and corticosteroids.
A renal biopsy, which showed tubulointerstitial inflammation, was performed. Immunohistochemical assays for several organisms were performed at CDC; the results were negative for hantavirus and spotted fever group rickettsiae, while immunohistochemical assay for leptospira showed granular immunostaining in the renal biopsy to confirm the diagnosis of leptospirosis (Figure 2B). The patient was discharged after 6 days on doxycycline 100 mg twice daily for 10 days and made a full recovery. Acute-phase serum was positive for leptospira IgM antibody by ELISA but negative for all serovars by microagglutination test at CDC. Convalescent-phase serum was positive for Leptospira by indirect hemagluttination assay at a private laboratory (Table 2).
The treating physicians in the 2000 New Melones outbreak initiated a public health inquiry to investigate potential environmental risks. This investigation identified potential sources of infection but did not identify a definitive source.
Five weeks after the New Melones exposures, a multidisciplinary team traveled to the reservoir to sample environmental sources for leptospires and to direct potential public health interventions. The physician for the first case, the state public health veterinarian, environmental health researchers from the University of California at Berkeley, and the local environmental health and sheriff's departments collaborated to better define the origins of this disease outbreak.
The team documented cattle herds grazing in the region above Wolf Gulch, where the three patients were presumed to have been infected. Leptospirosis is commonly transmitted following flooding that creates standing water in regions where cows or other animals graze. Though wildlife, including rodents, ungulates, and small carnivores, is common in this area, the proximity of the cattle and evidence that leptospirosis vaccination does not prevent shedding by cattle implicate these herds in the transmission of infection. However, the cattle were not tested for leptospiral antibodies because of their likely vaccination history. Furthermore, New Melones is a lake created by a dam of the Stanislaus River, and runoff between April and July is usually from snowmelt. After a warm, dry period of almost 3 weeks with temperature maximums in the high 70s and 80s, rain fell on May 6 and 7 totaling less than 1/2 inch. This weather shift could have provided the mechanism for contaminated animal urine to drain into the creeks surrounding the reservoir.
Using the Moore swab technique for water collection, the team collected 5 gallons of water from three sites in the reservoir, filtering them through sterile cotton plugs which were then incubated in leptospiral media (Ellinghausen McCullough Johnson Harris [EMJH] medium) at 29 C for several days. Though two of the three samples were positive for spirochetes upon darkfield microscopy, they were negative by polymerase chain reaction using primers specific for pathogenic strains of leptospira, a result of ambiguous significance in this case.