Leptospirosis is an uncommon disease that results from infection by one of the many serotypes of the spirochete Leptospira interrogans. In 1920, Takaki isolated Leptospira icterohemorrhagiae from a skunk for the first time in Korea¹⁾. Ro and others²⁾ reported acute hemorrhagic lung disease of unknown causes in the fall of 1975, and since then there have been subsequent reports^3,4). Although leptospirosis has long been thought to be present in Korea because of its occurrence in the neighboring countries of Japan, China and Taiwan⁵⁾, it was not until 1984 that leptospirosis in humans was documented by serology⁶⁾, by autopsy⁷⁾, and by isolation of causative organism⁸⁾.

Numerous combinations of symptoms and signs can occur. The degree of severity may vary from hepatorenal failure and meningitis associated with classic Weils disease to a mild flu-like illness. Leptospirosis is known to show protean clinical manifestations^3,4). The authors here describe a sudden outbreak of leptospirosis in Chonbuk Province in the fall of 1987.

Leptospirosis is one of the most common zoonoses in Korea today. It occurs worldwide, and the true prevalence of leptospirosis has never been known accurately, since the disease is under-suspected and under-diagnosed.

Humans contract it by coming into direct contact with infected animal tissue or with soil or water contaminated by leptospira-laden urine¹⁰⁾. The sudden outbreak of leptospirosis in September of 1987 seemed to be due to the wash-out of leptospira-laden rodents, urine into the fields where workers were tying up the fallen rice stalks after severe flooding⁴⁾. The outbreaks of leptospirosis in 1975, 1984, and 1985 also occurred after severe floods before the harvesting season^2,4). Table 1 shows the main three serogroups in the Chonbuk area. The most common was icterohaemorrhagiae in 1987, while in 1986 it was canicola. This suggests regional and yearly variations^11,12). Definite diagnosis depends upon either the isolation of the pathogen or, more commonly, the specific serologic test. Because a culture system is usually not available, serologic test is an easy mean of diagnosis. However, as shown in Table 2, one should take into consideration the fact that serological responses in humans were sometimes slow in rising, and in cases in which antibiotics have been given early in the infection, a detectable immune response was delayed or blunted^10,12,13).

All of the patients were farmers and their families who had worked in the fields more than once. Twenty percent of the patients sustained small cuts or abrasions on the hands and feet while working. These were ideal routes of leptospiral infection¹⁴⁾. One case of simultaneous infection of husband and wife was seen. Various studies of leptospirosis have shown that infected males outnumbered females several times^{9,11,12,15,16)}. Male predominance has been thought to be due to the factors of occupation and environment^11,16). As shown in Figure 1, this study showed the ratio of male to female to be 3:2. This increase in the female fraction was thought to be due to the increase of female workers in the fields, since many men were involved in damming up the flood or other repair work. As shown in Figure 2, there were overlapping periods of leptospirosis, hemorrhagic fever with renal syndrome, and scrub typhus. They needed careful differentiation because they were similar in early clinical manifestations, outbreak areas, time periods, and serologic tests.

Various combinations of symptoms and sings can occur during leptospira infection^{3,4,10,11,17,18)}. The most reliable clues for clinical diagnosis may be fever, muscle pain on stretching, and tenderness on palpation of the lower extremities, with or without hemoptysis. The authors clinically classified 54% of the patients as having the pneumonitis type, 49% as having the hepatitis type, 44% as having the nephritis type, and 13% as having the influenza type. The appearance of an influenza-like illness in the farmers of prevalent areas should alert practitioners of the possibility of leptospiral infection and the need to investigate these cases serologically. Our experience shows that leptospirosis in Korea is similar to that of China^3,19) but differs clinically from that of other countries^20,22). Overt meningitis was seen in only one patients. Abnormal liver function test was seen in 50% of the patients, 33% of which showed jaundice. No patient had renal failure severe enought to require dialysis. Hemoptysis was the predominant symptom. All fatal cases had chest lesions, and profuse, massive hemoptysis developed before death. The cause of death seemed to be asphyxia and acute respiratory failure. The mortality rate was 5% in this study, and was not related to age or to the severity of jaundice and renal failure, but to the severity of pulmonic lesion and massive hemoptysis. In three of the five fatal cases, the patients were transported over a long distance on unpaved roads. This may have been a causative factor, since in the prevention of hemoptysis absolute bed rest and avoidance of long-distance travel are important.

The pathogenesis of hemorrhagic pneumonitis is uncertain; since hemoptysis occurred in the early septicemic stage and a number of leptospira were found in the tissue of hemorrhahagic pneumonitis during autopsy, capillary damage by direct action of leptospiral toxins was suggested rather than disorders of the clotting mechanisms^20,23,24). It is interesting that the extent of the lesions on the chest X-rays did not always coincide with the presence or absence of hemoptysis, or with the amount of blood expectorated^23,24). Chest auscultation revealed less abnormal pulmonary findings than expected on radiologic studies^9,24). Ten (27%) of the 37 patients with hemoptysis had negative chest X-rays, and 11 (25%) of the 40 patients whose chest X-ray showed lesions did not have hemoptysis. As shown in Table 5, patients with hemoptysis showed lower hematocrit and platelet counts than those without hemoptysis. The severity of anemia was roughtly proportional to the amount of hemoptysis. The causes of anemia were thought to be blood loss, microangiopathy and hemoptysis²⁵⁾. Thrombocytopenia, which was seen in 18% of the patients in this study, is a well-known complication of leptospirosis whose pathogenesis remains uncertain²⁶⁾. The authors have tried to find a relationship between thrombocytopenia and renal failure and jaundice, but failed to note any correlation.

As shown in Table 4, the erythrocyte sedimentation rate increased in all of the patients in the acute stage, remained high during the illness, and then decreased after convalescence. The degree of elevation appeared not to reflect the severity of the disease.

The determination of serum creatine phosphokinase may be a simple test to help diagnose the acute phase of leptospirosis²⁷⁾. In this study, it was elevated in 30% of the patients. Nonspecific electrocardiographic abnormalities were observed in 46% of patients with leptospirosis^28,29), but the significance was not apparent.

Pulmonary function tests were performed in 25 cases. The abnormal findings included a mild obstructive pattern and a fixed obstructive pattern. All necropsies were performed just after death. The necropsy findings were similar to the previous reports in the Korean literature^7,30).

Doxycycline and penicillin are both effective in shortening the course of illness when they are given in the first four days of illness^31,32). Doxycycline, 100 mg once a week, will prevent leptospirosis in high-risk groups for three weeks³³⁾. Leptopiral vaccines have been available in Korea since 1988, but their effectiveness has not been determined. Control measures to eliminate the risks to farmers include vigorous rodent control, vigilant use of protective clothing, scrupulous personal hygiene, prophylactic use of doxycycline and possibly vaccines, and an awareness that leptospirosis is an occupational hazard, and that early diagnosis and prompt management can prevent a fatal outcome^14,34).