Public Health Surveillance After a Volcanic Eruption: Lessons from Cerro Negro, Nicaragua, 1992L

Public Health Surveillance after a Volcanic Eruption: Lessons from Cerro Negro, Nicaragua, 1992l

JOSEPHINEMALILAY,~ MARIANA GUIDO REAL,~ ALVARO RAM~REZVANEGAS: ERIC NOJI,~ & THOMAS SINKS*

444

The eruption of the Cerro Negro volcano near Lebn, Nicaragua, on 9 April 1992 distributed an estimated 1.7 million tons of ash over a 200 square kilometer area. An assessment was conducted to evaluate the health efjCectson approximately 300 000 residents, using routine data obtained by the national epidemiologic surveillance system. It was found that rates of visits to health care facilities for acute diarrhea1 and respiratory illnesses increased in two study communities, one within and one near the disaster zone. Specifically, visits for acute diarrhea were nearly 6 times more numerous than before the eruption in both communities, while visits for acute respiratory diseases were 3.6 times morefvequent in Malpaisillo (the community near the disaster zone) and 6.0 rimes morefiequent in Telica (the community within it). Most of the visits were for infants and children less than 5 years old. Increased diarrhea1 disease morbidity, which commonly occurs after volcanic eruptions, de- mands detailed investigation of the type and quality of water supplies following heavy ashfall. Ash-related respiratory problemsshould be further examined to determine the spectrum of such diseases and the timing of illness onsets among infants and other special population subgroups. Data collected on health conditions beforeand after an eruption by passive surveillance can be used to detect eruption-related morbidity. Systems already in place, such as Nicaragua’s national epidemiologic surveillance system, can be modified or extended so as to increasetheir sensitivity to new cases and hencetheir ability to provide appropriate not&ation to medical relief agencies.

nvestigation of the health effects of di- related problems for the purpose of mount- I sasters with acute impacts has tended to ing relief operations (7). However, the work employ active surveillance systems-ones reported here made use of a passive sur- that actively solicit information as opposed veillance system, Nicaragua’s national dis- to passive (routine) surveillance systems ease surveillance system, to detect health that do not (1-6). Such active systems can effects following a volcanic eruption and permit immediate assessment of disaster- identify issues whose resolution could re-

1The work reported here was funded by a contractual 770-488-7335). This article will also be published in agreement [APO-43482 (RR)] with the Emergency Spanish in the Revista Panamericana de Salud Mblica/ Preparedness and Disaster Relief Coordination Pan American Journal ofPublic Health, Vol. 1,1997. Program of the Pan American Health Organization, 2Division of Environmental Hazards and Health Washington, D.C., U.S.A. Reprint requests and other Effects, National Center for Environmental Health, correspondence should be addressed to Josephine Centers for Disease Control and Prevention, Atlanta, Malilay, Epidemiologist, Health Studies Branch (F-46), Georgia, U.S.A. Division of Environmental Hazards and Health 3 Sistema Local de Atencibn Integral en Salud, Ministry Effects, National Center for Environmental Health, of Health, LeBn, Nicaragua. Centers for Disease Control and Prevention, Atlanta, 4 National Epidemiologic Surveillance Unit, Ministry GA 30341-3724, USA. (Telephone 770-488-7350; Fax of Health, Managua, Nicaragua.

218 Bulletin of PAHO 30(3), 1996 duce morbidity from volcano-related haz- 1). Initially, local health authorities ex- ards. The results obtained served to dem- pressed concern about hazards posed by onstrate that, with modification, routine toxic gases-because sulfur dioxide con- health information systems such as the na- centrations were reported nine times higher tionwide surveillance system employed than normal. Although no casualties were can provide reasonable estimates of post- reported, 300 000 people living in the af- disaster health problems. fected zone were at risk, more than 10 000 of whom required some emergency assis- BACKGROUND tance (9, 20).

Nicaragua’s Cerro Negro volcano (12.51 O MATERIALS AND METHODS N, 86.70” W), located approximately 25 kilometers northeast of the provincial capi- Weekly summaries of reportable ill- tal of Leon, erupted at 11:30 p.m. on 9 April nesses and deaths for the month before the 1992 (8). Over the next three days an erup- eruption were obtained from the Informe tion plume deposited an estimated 1.7 mil- diario de vigilancia epidemiol@ica, the report- lion tons of ash in a west-southwesterly ing vehicle of the Local System of Integral direction over an area of 200 square kilo- Health Care (Sistema Local de Atencih Inte- meters extending beyond Leon, some 80 graZ en Salud -SKAIS), this latter being the kilometers northwest of Managua (Figure health information reporting unit of Leon Province. Using the same information source, we also obtained daily reports of Damage from volcanic ashfall within the study illnesses and deaths for a one-week period area. following the eruption. Each day nine provincial municipalities and the city of Leon reported morbidity and mortality statistics from all of their respective hospitals, health clinics, and health posts. From among these 10 reporting subdivisions we selected two, Malpaisillo (population 35 692) and Telica (population 22 378), that encompassed about 48% of the province’s area and included most of its population outside the city of Leon. Age-specific break- downs of these two municipalities’ populations were readily available (II). We determined morbidity only for acute diarrhea1 and respiratory illnesses in these communities, because we observed only sporadic instances of other conditions (such as conjunctivitis, measles, and suspected cholera cases) during the study period. For purposes of the study, we examined cases said to have occurred during the epidemiologic reporting period of 8 March-4 April 1992 (before the 9 April eruption) and those reported for 12-18 April after the eruption. Case definitions for acute diarrhea1 disease

Malilay et al. Health Surveillance 219 Figure 1. A map showing levels of ashfall from the 9 April 1992 eruption of the Cerro Negro volcano, the altitude of surrounding territory, and the locations of the principal capital, Lebn; the two study communities, Malpaisillo and Telica; other nearby towns; and other nearby volcanoes, indicated by “v”.

87”OO’ 8630’ Elevationrn meters q q n 100-200 ZOO-600 600-l 000 1 000-l 500 1 500-Z 000

Source: Nicaraguanlnstrtute 01 Terrrtorral SIudres (Inshiulo Mcaraguense de Estudm Tern/ma/es)

and acute respiratory infections were not 23.2 per 1000 one week after the eruption. available from the surveillance system. Weekly rates of health care visits for diarrhea1 disease in the community of RESULTS Malpaisillo tended to be considerably higher than in Telica (Figure 2). Weekly rates of health care visits for Before the eruption, weekly rates of acute diarrhea1 disease were highest among health care visits for acute respiratory ill- children younger than 1 year of age, with ness were higher in Malpaisillo than in visit rates increasing from 13.8 per 1 000 Telica. Noteworthy increases in these rates during the month before the eruption to were observed in both communities after 45.1 per 1000 one week after the eruption. the eruption, that in Telica being more than In terms of age, the next highest weekly fourfold. During the study period, infants rates for such visits occurred among chil- (especially) and children under 5 years old dren 1 to 4 years old, among whom these consistently exhibited higher rates of acute visit rates increased from 2.3 per 1 000 respiratory infection than all other age during the month before the eruption to groups in either community. Among in-

220 Bulletin of PAHO30(3),1996 Figure 2. Weekly rates of reported health care Figure 3. Weekly rates of reported health care visits per thousand for acute diarrhea1 diseases visits per thousand for acute respiratory diseases among infants and young children in the among infants and young children in the municipalities of Malpaisillo and Telica, municipalities of Malpaisillo and Telica, Nicaragua, from 8 March through 18 April Nicaragua, from 8 March through 18 April 1992. 1992. loa- 80 - :

60-

.-_.-.- 0 I 1 1 I I March 15-Z Z-28 March29- 5-11 12118 March 15-21 22-28 March29- 5-11 12-18 &14 April4 a14 April4

Agegroup, III years Agegroup, in years - ~1, Malpaisillo --- 1-4, Malpalsillo -

fants, the weekly rates of health care visits Among infants, observed acute diarrhea1 in Malpaisillo for acute respiratory illness disease morbidity was roughly three to four ranged from 27.7 per 1000 four weeks be- times greater after the eruption in both fore the eruption to 79.9 per 1000 one week study communities. However, among chil- after the eruption. In Telica, these rates dren 1 to 4 years old, the observed morbid- ranged from 17.4 per 1000 four weeks be- ity was 5.9 times higher after the eruption fore the eruption to 83.6 per 1000 one week in Malpaisillo (95% CI: 4.3, 8.2) and 17.3 after the eruption (Figure 3). times higher in Telica (95% CI: 7.1, 42.1). We compared diarrhea1 and respiratory For all other age groups, the relative risk of morbidity before and after the eruption for experiencing acute diarrhea1 disease after proportional increases in the rates of dis- the eruption ranged from 10 to 30 in ease associated with the eruption. Tables 1 Malpaisillo and 3 to 7 in Telica. In general, and 2 show standardized morbidity ratios the apparent risk of acute diarrhea1 disease (SMR) and 95% confidence intervals (CI) for was higher in Malpaisillo than in Telica for acute diarrhea1 and respiratory illnesses all age groups, except for children between among those in the study communities (12). the ages of 1 and 4. Using preeruption age-specific morbidity Compared to preeruption morbidity, the in each community as a standard, we found apparent relative risk of experiencing acute that morbidity from acute diarrhea1 disease respiratory illness (ARI) after the eruption after the eruption in both communities was was 3.6 in Malpaisillo and 6.0 in Telica. 5.8 times higher than expected. Similarly, Within the specific age groups studied (see observed morbidity from acute respiratory Table 2), observed ARI morbidity increased illness after the eruption was 3.6 times by factors ranging from 2 to 10. The rela- higher than expected in MalpaisilIo and 6.0 tive risks of ARI after the eruption (as com- times higher in Telica. pared to before the eruption) were consis-

Malilay et al. Health SuweiZIance 221 Table 1. Acute diarrhea1 disease cases among people visiting Malpaisillo and Telica health facilities before and after the eruption, showing standardized morbidity rates (SMR) and 95% confidence intervals derived from these data.

Age Population Preeruption Expected Observed group, projection, morbidity No. of No. of in years 1992 per 1 000 cases* cases+

Ma/paid/o:

Total 34.0 198 SMR (95% confidence interval): 5.8 (5.0, 6.7)

Telica:

Total 8.5 49 SMR (95% confidence interval): 5.8 (4.3, 7.5)

*Based on data for 8 March-4 April 1992. +12-18Apr1l 1992.

tently higher for all age groups in Telica cases may not have prompted visits and than for their counterparts in Malpaisillo, there could have been repeat visits to the these risks ranging from 3.7 (95% CI: 2.7, health care facilities involved. 5.0) to 10.0 (3.1,31.9). We also detected cases Even though residents were evacuated of acute diarrhea, ARI, and conjunctivitis from affected areas, the numbers of health among persons living in evacuation camps; care visits increased during the week after but no noteworthy trends in daily morbid- the eruption. Since the evacuated people had ity were found during the 10 days imme- not yet returned to their homes in these ar- diately after the eruption. eas, the numbers of health care visits after the eruption probably underrepresented di- DISCUSSION arrheal and respiratory disease morbidity. More specifically, residents of the mu- Epidemiologic surveillance in municipal nicipalities of Malpaisillo and Telica were health clinics indicated that weekly rates of evacuated to an estimated 20 shelters out- health care visits for acute diarrhea1 and side the affected zone, along with people respiratory illnesses increased after the from Leon, La Paz Centro, Quezalguaque, eruption, particularly among children un- Corinto, Chichigalpa, and several areas der 4 years old. These weekly rates of health within a 12kilometer radius of the volcano. care visits provided only an approximation These residents went to temporary shelters of disease incidence, since some disease in Leon within three days after the erup-

222 Bulletin ofPAH0 30(3), 2996 Table 2. Acute respiratory disease cases among people visiting Malpaisillo and Telica health facilities before and after the eruption, showing standardized morbidity rates (SMR) and 95% confidence intervals derived from these data.

Age Population Preeruption Expected Observed group, projection, morbidity No. of No. of in years 1992 per1 000 cases* cases+

Malpaisillo:

Total 198.8 710 SMR (95% confidence interval): 3.6 (3.3, 3.8)

Telica:

Total 58.3 352 SMR (95% confidence interval):6.0 (5.4, 6.7)

*Based on data for 8 March-4 April 1992. +12-18April 1992.

tion and were moved a day later to encamp- ter are wells, conditions predisposing to ments in surrounding areas. Evacuees re- diarrhea1 diseases may be created or exac- ceived medical attention provided by four erbated indirectly by the effects of ashfall health posts that were established within on water supplies. These conditions, these encampments (9). coupled with poor sanitation and hygiene Although gastrointestinal illnesses are in rural areas, could explain the increased not caused directly by volcanic eruptions, diarrheal disease rates observed. such illnesses have been reported as sec- Ash-related ocular and respiratory prob- ondary effects arising from unfiltered, in- lems have been reported in the aftermath adequately chlorinated surface water. of volcanic eruptions (3,14-21). Immedi- Waterborne giardiasis has been associated ate effects have included transient, acute with heavy water runoff resulting from irritation of the mucous membranes of the warm weather and volcanic ashfall on eye and respiratory tract by volcanic ash snow (23). Heavy ashfall also has been and gases as well as exacerbation of exist- known to affect the operation of sewage ing chronic lung diseases by heavy ashfall treatment plants by overwhelming filter during and for some time after the erup- beds, damaging machinery, and diverting tion (15). Within one hour of the beginning raw sewage into surface water (24). In ru- of volcanic activity at Cerro Negro, ash be- ral settings, where the main sources of wa- gan falling in Ledn. By the next day, depos-

MuMay ef al. Health Surueillance 223 its of up to 1 cm were recorded. As of 12 of the ashfall and evacuees at nearby en- April, changes in wind direction from the campments who may have received medi- west-southwest to the west (see Figure 1) cal attention outside of health posts estab- led to accumulations of an estimated 2.5 cm lished within the encampments. At the of ash in Telica (22). same time, Malpaisillo’s health facilities Overall, the eruption led to a two- to ten- continued providing services to surround- fold increase in health care visits for acute ing communities that were not affected by respiratory disease among residents of the eruption. This population could have Malpaisillo and Telica within the age contributed to increased visit rates as a re- groups studied. High rates of ARI observed sult of events other than the eruption. among study population infants could be Ideal comparison periods for assessing attributable to a number of circumstances, the impact of the eruption would have been including infections in crowded shelters epidemiologic reporting periods from pre- that may have been treated at clinics in the vious years, particularly the last five years, study areas soon after the eruption, before that were identical to the posteruption health posts were established in the evacu- study period. However, these data were not ation settlements. It is also conceivable that available at the time of the investigation, a new onset of respiratory illness may have and thus we were unable to determine ex- occurred. (Following a 1979 eruption of the cess morbidity. Overall, it was difficult to La Soufriere volcano on the island of St. determine from the data gathered whether Vincent, transient bronchospastic airway increased health visits for respiratory and disease was observed for the first time diarrhea1 diseases, as detected by the sur- among previously well infants--15,23.) veillance system, were due to health effects Before the eruption, weekly rates of vis- of the eruption rather than to increased visits to health care facilities indicated higher its by persons who availed themselves of diarrhea1 and respiratory disease morbid- health services after the eruption. Never- ity in Malpaisillo than in Telica. After the theless, the results of this investigation eruption, apparent increases in nonspecific point up the potential usefulness of routine diarrhea1 and respiratory illnesses were health information systems in obtaining noted in both communities; however, po- worthwhile information about the inci- tentially confounding factors related to the dence of selected diseases after a disaster. characteristics of the study communities and coverage by the health centers serving CONCLUSIONS them must be noted. We attributed the higher posteruption Obviously, volcanic eruptions can have rate of health care visits for acute respira- both direct and indirect, as well as imme- tory conditions in Telica, 16 kilometers west diate and delayed impacts upon health and of the volcano, to its location in the path of safety (15). The effects of these events can the ashfall (see Figure 1). Compared to be actively monitored via existing national Telica, the municipality of Malpaisillo is surveillance systems to provide useful in- located several kilometers north of Cerro formation about health changes in the Negro, outside the perimeter of major populations at risk. Concurrently, passive ashfall. Even so, the increased diarrhea1 and surveillance-such as that performed by respiratory disease morbidity in Malpaisillo the national surveillance system in the that was indicated by higher rates of health work reported here-can be used to center visits may have been partly due to supplement active surveillance in monitor- the eruption. Health centers may have ing health effects over a wider area or for a treated both residents living within the path longer time period.

224 Bulletin of PAHO 30(3j, 2996 In view of the findings reported here, we disasters in Guatemala. Disasters 1978;2: recommend further investigation of the fol- 39-46. lowing matters: 5. Dietz VJ, Rigau-Perez JG, Sanderson L, Diaz L, Gunn RA. Health assessment of the 1985 flood disaster in Puerto Rico. Disasters (a) Ash-related respiratory diseases. 1990;14:164-170. Detailed studies should be conducted to 6. Lee LE, Fonseca V, Brett KM, et al. Active assess the spectrum of such diseases and morbidity surveillance after Hurricane determine their time of onset among spe- Andrew: Florida, 1992. JAMA 1993;270:591- cial subgroups such as infants within the 594. population. 7. Glass RI, Noji EK. Epidemiologic surveillance following disasters. In Halperm W, (b) The type and quality of water sup- Baker EL Jr, eds. Public health surveillance. plies in rural areas. The marked increase in New York: Van Nostrand Reinhold; 1992: acute postdisaster diarrheal diseases, par- 195-205. ticularly among young children, calls for 8. Smithsonian Institution. Cerro Negro. Bull further study of the water supply. Global Volcanism Network 1992;17(4):7-9. (c) The national epidemiologic surveil- 9. Naciones Unidas. Emergencia eruption lance system. The system could be modified “Volcan Cerro Negro.” Managua: NU; April 1992. or extended so as to increase its sensitivity 10. Pan American Health Organization. Volume to new cases and hence its ability to provide I: health conditions in the Americas. 1994 ed. appropriate notification to medical relief Washington, DC: PAHO; 1994. (Scientific agencies. The system could also be modified publication 549). to examine the long-term effects of exposure 11. Census projections, Department of Le&z, Nica- to ash in a particular community. ragua. Leon: Ministerio de Salud (MINSA), Sistema Local de Atencion Integral en Salud; 1992. Acknowledgments. We thank the fol- 12. Vandenbrouke JR A shortcut method for lowing for supporting this work: Dr. Au- calculating the 95 per cent confidence inter- rora Velasquez and Ms. Maritza Montalban val of the standardized mortality ratio. Am of SILAIS, Leon, Nicaragua; Dr. Stanley J Epidemiol 1984;115:303-304. Williams of Arizona State University, 13. Weniger BG, Blaser MJ, Gedrose J, Lippy EC, U.S.A.; Dr. Peter Baxter, Cambridge Univer- Juranek DD. An outbreak of waterborne gi- sity, U.K.; Dr. Claude de Ville of PAHO, ardiasis associated with heavy water runoff due to warm weather and volcanic ashfall. Washington, D.C.; and PAHO/Nicaragua. Am J Public Health 1983;8:868-872. 14. Baxter PJ, Bernstein RS, Falk H, French J, Ing REFERENCES R. Medical aspects of volcanic disasters: an outline of the hazards and emergency re- Thacker SB, Berkelman RL. Public health sponse measures. Disasters 1982;6(4):268- surveillance in the United States. Epidemiol 276. Reu 1988;10:164-190. 15. Bernstein RS, Baxter PJ, Buist AS. Introduc- Pan American Health Organization. Epide- tion to the epidemiological aspects of explo- miologic surveillance after natural disaster. sive volcanism. Am 1 Public Health 1986; Washington, DC: PAHO; 1982. (Scientific 76(suppl):3-9. publication 420). 16. Seaman J, Hogg C. Volcanoes. In Seaman J, Bernstein RS, Baxter PJ, Falk H, Ing R, Fos- Lewesley S, Hogg C, eds. Contributions to ter L, Frost E Immediate public health con- epidemiology and biostatistics, Volume 5. Basel, cerns and actions in volcanic eruptions: les- Switzerland: S. Karger; 1984157-172. sons from the Mount St. Helens’ eruptions, 17. Baxter PJ, Ing R, Falk H, Plikaytis 8. Mount May 18-October 18,198O. Am JPubZic Health St. Helens eruptions: the acute respiratory 1986;76(suppl):25-38. effects of volcanic ash in a North American Romero AB, Cobar R, Western KA, Mayorga community. Arch Environ Health 1983;38(3): L6pez S. Some epidemiologic features of 138-143.

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Sanita y Engineering Congress to Meet in Mexico

The XXV Inter-American Congress of Sanitary Engineering and Environ- mental Sciences will be held 3-7 November 1996 in Mexico City. Spon- sored by the Inter-American Association of Sanitary Engineering (AIDIS), the meeting is expected to draw over 1500 participants from the countries of the Americas. One of the main events at the XXV Inter-American Congress will be Expo Environment ‘96, where individuals as well as private and public institutions will display the latest in technical developments, programs, products, and services in the field of environmental protection. In addi- tion, there will be panel discussions and plenary sessions featuring technical papers in the fields of water and wastewater treatment and reuse, solid waste management and disposal, air pollution control, and environmental impact assessment. Requests for more information should be directed to: Calzada de Tlalpan #972, Colonia Nativitas, C.P. 03500 Mexico, DE., M&&o; telephone (5-25) 579-4809,579-6723, or 579-5482; fax (5-25) 537-0813.

226 Bulletin of PAHO 30(3J, 1996