Two outbreaks of enterically transmitted non-A, non-B (ET-NANB) hepatitis occurred during the late summer and fall of 1986 in rural villages in the State of Morelos, Mexico. This is the first reported instance of epidemic transmission of this disease in the Americas.

Huitzililla, Morelos. In September 1986, an outbreak of hepatitis among adult residents of Huitzililla, Morelos, was reported to the Mexican Secretariat of Health. A census of the 1,757 inhabitants of this rural town identified 94 persons who had developed an illness with jaundice since June 1. Onsets were between June 5 and October 16, and the overall attack rate was 5%. The outbreak lasted 20 weeks, with the peak incidence in the second week of August (Figure 1). The first case occurred about 1 month after the seasonal rains began. Ninety-eight percent of the patients had anorexia and discolored urine; 97% had malaise; 87%, abdominal pain; 78%, arthralgias; and 53%, fever. Five of the six patients for whom sera were tested had abnormal liver-function tests (alanine aminotransferase (ALT)). Two patients, both nonpregnant adult women, died. One patient was a woman in the third trimester of pregnancy; neither she nor her infant suffered any detectable complications.

The attack rate was significantly higher for persons over 15 years of age (10%) than for younger persons (1%) (pless than 0.01) but did not vary significantly by sex. Attack rates by block of residence in the town varied widely and ranged from 0% to 29%, with the highest rates being in blocks that bordered on two small streams.

The town has no system for disposal of human feces, and, at the time of investigation, human fecal material was present on the banks of both streams. The wells of families living next to the streams were very shallow (3 to 6 feet). Nineteen (56%) of the 34 well-water samples tested exceeded 2 fecal coliforms per 100 ml.

A case-control study was carried out to determine risk factors associated with illness. Thirty-two patients who had the initial case of hepatitis in their families were compared with 19 persons from families without illness. Illness was highly associated with water-related factors: families with illness were more likely than families without illness to have well-water with visible turbidity or particulate matter (91% compared with 21%; odds ratio (OR) = 36.3; 95% confidence interval (CI), 5.9 to 278.1); families with illness were less likely to have wells with protective walls (38% compared with 84%; OR = 0.11; 95% CI, 0.03 to 0.54) and were less likely to boil water for drinking (23% compared with 56%; OR = 0.23; 95% CI, 0.05 to 0.96). Contact with an ill member of a different household was also a significant risk factor. Other factors, such as consumption of specific foods and receipt of injections, were not associated with the risk of hepatitis.

Sera were collected from 62 patients and stools from 8 patients with recent onset of disease. Sixty (97%) of the serum samples were positive for antibody to hepatitis A virus (anti-HAV), but none had measurable IgM anti-HAV. None were positive for hepatitis B surface antigen (HBsAg); five (9%) were positive for antibody to hepatitis B core antigen (anti-HBc), but none were positive for IgM anti-HBc. Stool specimens were examined by immune electron microscopy (IEM) using sera from Asian patients with known ET-NANB hepatitis and sera from patients in this outbreak as an antibody source. Three of the 8 stools were positive for 28- to 34-nm viruslike particles similar to those seen by IEM in cases of ET-NANB hepatitis from Central Asia, Nepal, and Burma. In addition, a pool of the first four serum samples tested aggregated non-A, non-B hepatitis viruslike particles obtained from a patient during a recent outbreak in the Soviet Union.

Telixtac, Morelos. In October, while the outbreak in Huitzililla was being investigated, a cluster of hepatitis cases among young adults was reported from Telixtac, Morelos. Telixtac is a small rural community of 2,194 inhabitants about 30 miles from Huitzililla. A census identified 129 persons who had developed jaundice since June 1. Onsets were between August 20 and January 9, and the overall attack rate was 6%. This outbreak lasted 21 weeks, with the peak incidence occurring during the third week of September (Figure 2). The first case occurred about 3 months after the beginning of the seasonal rains in May. Ninety-three percent of the patients had discolored urine; 91% had malaise; 90%, anorexia; 85%, abdominal pain; 81%, arthralgias; and 62%, fever. All three patients for whom sera were tested had abnormal liver-function tests (ALT). One person, an adult nonpregnant woman, died. One pregnant woman was ill; she made an uneventful recovery, but, 15 days after onset of icterus, she delivered a premature infant of 32 weeks gestation. The infant weighed 2.2 kg and died at 3 months of age of unknown causes.

The attack rate was significantly higher for persons over 15 years of age (10%) than for younger persons (2%) (pless than 0.01) and did not vary by sex. Attack rates varied from 0% to 40% by block of residence.

At the time of the investigation, most families were getting their drinking water from deep irrigation wells located at the edge of the community. However, during the May through September rainy season, many families had gotten water from two small streams that run through the center of the village but that are dry most of the year. Like Huitzililla, Telixtac has no system for disposal of human feces.

A case-control study similar to the one in Huitzililla was performed. Fifty-four patients who had the initial case of hepatitis in their families were compared with 67 persons from families without illness. Families with illness were more likely than families without illness to obtain drinking water from the local stream (20% compared with 2%; OR = 16.9; 95% CI, 2.1 to 98.1); families with illness were also more likely to use stream water for cooking and washing dishes (16% compared with 2%; OR = 12.6, 95% CI, 1.5 to 84.6). No risk could be demonstrated for obtaining drinking water from any of the deep wells. Contact with an ill person outside the household was also a risk factor for illness, but other factors, such as consumption of specific foods, attendance at social events, and receipt of injections, were not significantly different between patients and controls.

Sera were collected from 53 patients and stools from 8 patients with recent onset of disease. All serum samples were positive for anti-HAV antibody; only two (4%) had detectable IgM anti-HAV. None were positive for HBsAg; only one was positive for anti-HBc, but this serum was negative for IgM anti-HBc. The same IEM technique used to evaluate the stool samples from the Huitzililla patients was used in studying this outbreak. Numerous 28- to 34-nm viruslike particles similar to those detected for the Huitzililla and Asian patients with ET-NANB hepatitis were identified in one stool. These viruslike particles were aggregated by sera from the Huitzililla and Asian patients. Reported by: C Tavera, Secretariat of Health, State of Morelos; O Velazquez, MD, C Avila, MD, G Ornelas, MD, C Alvarez, MD, Field Epidemiology Training Program; J Sepulveda, MD, Director, Div of Epidemiology, Secretariat of Health, Mexico. Field Epidemiology Training Program, International Health Program Office; Hepatitis Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Non-A, non-B hepatitis is caused by at least two distinct viral agents with different modes of spread. The first, post-transfusion non-A, non-B hepatitis, is epidemiologically similar to hepatitis B and is believed to be the most common type of non-A, non-B hepatitis in North America and Europe. The second, ET-NANB hepatitis, is transmitted by the fecal-oral route and has caused large outbreaks in India (1,2), Nepal (3), Burma (4), Pakistan (5), and the Soviet Union (6). More recently, ET-NANB outbreaks have been reported from Africa (7,8). Although person-to-person transmission takes place, most of this epidemic transmission has occurred following heavy rains in populations with inadequate sewage disposal. Mortality rates for pregnant women have been as high as 20% in many of the large outbreaks (3,8).

As in other large outbreaks, disease transmission via contaminated water was important in both Mexican outbreaks. It was most apparent in Huitzililla, where the outbreak coincided with seasonal rains, and the shallow, poorly protected wells were easily contaminated with inadequately disposed human feces. The outbreak in Telixtac differed in that, even though it began during the seasonal rains when impure stream water was available, only a minority (20%) of patients used this water source. Thus, the majority of cases in Telixtac may have resulted from person-to-person transmission.

In almost all reported outbreaks of ET-NANB hepatitis, clinical illness is much more common among adults than among children. In most outbreaks, it is likely that children and adults have been exposed at comparable frequencies and that the observed differences in rates of clinical illness are due to differential expression of disease by age similar to that seen for hepatitis A. The occurrence of a large

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