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Investigation of outbreak of Andaman Haemorrhagic Fever
 

Outbreaks of a febrile illness with haemorrhagic manifestations and high case fatality ratio occurred in South and North Andaman in 1988. The etiology of the disease could not be identified and it was named as Andaman Haemorrhagic Fever. The empirical treatment regimen used was crystalline penicillin and chloramphenicol. Patients who reported early to the hospitals responded well to this regimen. However, a significant proportion of the patients developed fatal pulmonary haemorrhage. The outbreak disappeared soon, reappeared the next year. Investigations were carried by various research agencies and the probable etiologies suggested by these investigating teams were Hantaa virus, Ricketsia tsutsugamushi, Yersinia pestis etc. However, no virus or rickettsia could be isolated from the clinical specimens taken from the patients.

 During the period 1988 – 93, the outbreak had occurred every year during the post monsoon period. Year-wise cases and deaths are shown in table 1. Disease occurrence had an association with rainfall. Quarter-wise rain fall and number of reported cases is shown in figure 1. In North Andaman, the disease was mainly affecting farmers and children and adolescents in the families of farmers. The commonest age group of the patients was 20 – 24 years in 1988. However, this was showing a shift towards lower age groups during subsequent years and in 1993 the commonest age group was 5 – 9 years. The mean age of patients in 1988 was 24.2 y (SD: 12.9 y) and that in 1993 was 14.4 y (SD: 12.5 y).

  Table 1. Year-wise cases and deaths due to Andaman Haemorrhagic Fever in Andaman islands during 1988 – 93  

 

Year

Cases

Deaths

CFR

 

 

1988

90

27

30.0%

 

 

1989

92

10

10.9%

 

 

1990

22

6

27.3%

 

 

1991

48

15

31.3%

 

 

1992

6

3

50.0%

 

 

1993

52

9

17.3%

 

 

Total

310

70

22.6%

 

Historically, Andaman islands are known to be endemic to leptospirosis. The first report of bacteriologically confirmed leptospirosis in India was from South Andaman in 1929. Leptospirosis had a high incidence among the free living convicts during 1920s and 30s. Disease incidence was showing the same seasonal trend as the outbreaks of AHF in recent years. Areas of occurrence of leptospirosis during 1920s in South Andaman were the same as those affected by AHF outbreaks.

Although the clinical presentation of AHF was different from the classical presentation of leptospirosis viz Weil’s syndrome, because of the epidemiological similarities between the outbreaks of AHF and the earlier occurrence of leptospirosis in South Andaman, it was considered worthwhile to investigate the possibility of a leptospiral etiology of AHF. In October 1993 an outbreak of AHF occurred in Diglipur in North Andaman. Thirty-nine patients suspected to have AHF were admitted to the Community Health Centre (CHC), Diglipur. Thirty-three of these 39 patients recovered and six died giving a case fatality ratio of 15.4%. Blood samples were collected during acute phase from 30 patients. Convalescent samples were collected from 23 patients. These samples were tested for anti-leptospiral antibodies using Microscopic Agglutination Test (MAT) with 13 strains of live leptospires representing 12 serogroups.

 

Sero-conversion or four-fold rise in antibody titre was demonstrated in 18 of the 23 patients with paired sera. Two of the seven patients with only a single sample also had antibody titres ≥ 1 in 100. Most of the patients who tested positive had antibody titre against serogroup Grippotyphosa. The other serogroups against which antibodies were demonstrated include Canicola, Australis and Icterohaemorrhagiae.

AHF was the first report of leptospirosis with pulmonary complication from India. Severe pulmonary haemorrhage is now recognized as an important fatal complication of leptospirosis. It has been observed in other countries such as China, Korea and other South East Asian countries and in Nicaragua in South America. Because of the unusual clinical presentation of the disease AHF remained as a diagnostic mystery for five years. The results of the investigation, thus, solved this diagnostic enigma.

Fig 1. Quarter-wise rainfall and number of reported cases of leptospirosis in Andaman Islands during 1988 – 93