Aedes survey of selected public hospitals admitting dengue patients in Metro Manila, Philippines Estrella Irlandez Cruz#, Ferdinand V. Salazar, Wilfredo E. Aure, Elizabeth P . Torres Department of Medical Entomology, Research Institute for Tropical Medicine, Department of Health, Filinvest Corporate City, Alabang, Muntinlupa City, Metro Manila, Philippines
Abstract Entomological investigations were carried out in five selected public hospitals admitting dengue patients in Metro Manila, Philippines. The results revealed the presence of only one species, i.e. Aedes aegypti, mostly breeding in fresh water plant vases, drums, basins, plastic cups, tin cans, and empty paint cans. The water plant vase/bowl was found to be the most preferred container for Ae. aegypti breeding. The percentage positive rates of fresh water plant vases of the five public hospitals were: RMC (40.69%), TMC (76.62%), SLH (80.60%), NCH (64.06%), and EAMC (40.40%). An analysis of data revealed that the Premise, Container, and Breteau indices varied from 0.0 to 4.0, 0.0 to 41.1 and 0.0 to 11.0 respectively, indicating thereby the high receptivity of the area to DF/DHF transmission. The egg density ranged from 0.0 to 48.5 which showed the presence of Ae. aegypti vector in the five public hospitals. The presence of productive breeding sites indoors and outdoors in the study area revealed that outbreaks could possibly occur in the future if no vector control plan is adopted and implemented. Keywords: Aedes aegypti; Hospitals; Receptivity; Ovitrap index; Philippines.
Introduction The Philippines is one of the dengue endemic countries in Asia. Since the first outbreak of dengue fever (DF) and dengue haemorrhagic fever (DHF) in 1953[1], Philippines has been experiencing an increasing incidence of dengue cases. Based on the data of the National Epidemiology Centre of the Department of Health[2], there were 12 900 cases in 1997, 35 600 in 1998, 9221 in 1999, 8761 in 2000 and 25 050 cases in 2001. #
Entomological surveys of communities have been conducted in the Philippines since the development of the Dengue Prevention and Control Programme (DPCP) of the Department of Health was initiated. The increase and peak in the number of dengue cases were observed to coincide with the rainy months of August to November, and the Aedes aegypti density was the highest during this period, while the months of February to April are low-density months. In 1993, Schultz[3], in his study on the seasonal abundance of dengue, confirmed that Ae.
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aegypti was the major container breeder in residential areas while Ae. albopictus predominated in cemeteries in Manila. In view of the high vulnerability of major hospitals, which admit dengue patients, no study has been carried out to assess the receptivity for Ae. aegypti. The present study was conducted in five major hospitals during September 2001 to April 2002 and the results are incorporated in the present communication.
The level of infestation of Ae. aegypti mosquitoes, i.e. Premise (House) Index (PI), Container Index (CI) and Breteau Index (BI), was estimated as per WHO guidelines[4].
Ovitrap survey The ovitrap was made from a tin can 76.2 mm in diameter, 101.6 mm in height, and painted black inside and outside. Water was added to a level of 76.2 mm. A wooden paddle (25.4 mm x 152.4 mm) was placed diagonally inside the tin can with the rough surface on top. The paddle served as oviposition substrate. The number of ovitraps used was calculated through sequential sampling (Lee, 1987) [5]. Thirty ovitraps were set up indoors of hospitals and 30 ovitraps were placed outdoors. “Indoors” refers to the interior of the room while “outdoors” refers to the outside of the hospital building but within the hospital compound. The ovitraps were set up at different strategic places indoors – under the sink, in the corner of rooms, under the cabinet, under the bed, inside the comfort room, in the hospital chapel, and the nurse station; while outdoors, these were placed in corners of the hospital building, in the parking area, near vegetation, near piles of wood/hollow blocks, and plants/trees in the garden. Lost or damaged ovitraps were replaced regularly. The ovitraps were collected after seven days with the water and paddle placed separately in plastic bags. The eggs were counted in all positive ovitraps. Plastic bags of positive ovitraps were submerged into a pan for larval emergence. The larvae were counted and identified for species confirmation. Similarly, the collected paddles were submerged into a pan with water for larval emergence. Fish flakes were used as larval food. The third and fourth instar larvae were identified for confirmation of species.
Study area An entomological survey of dengue vectors was conducted in five selected public hospitals in Metro Manila, which had the highest number of dengue admissions for five years (1995– 2000) based on the Department of Health (DOH) – National Capital Region (NCR) Surveillance data 1995–2000[2]. These were: San Lazaro Hospital (SLH), Rizal Medical Centre (RMC), Tondo Medical Centre (TMC), East Avenue Medical Centre (EAMC) and National Children’s Hospital (NCH).
Methodology Aedes larval/pupal survey A total of 500 rooms were surveyed monthly for Ae. aegypti in the five selected hospitals. Larval/pupal survey was done monthly for six months. The survey for Ae. aegypti mosquito breeding was carried out using the single larva techniques. The larvae/pupae were collected from all infested containers and identified in the laboratory for species identification. Subsequently, water was removed to destroy the foci of breeding.
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Analysis of data The PI, CI and BI were computed using the WHO guidelines. At the same time, the Ovitrap Index and Ovitrap Density Index were computed.
Results and discussion The monthly averages of Premise Index (PI), Container Index (CI) and Breteau Index (BI) of San Lazaro Hospital (SLH) varied from 0 to 2, 5 to 25 and 2.0 to 8 respectively; in the Tondo Medical Centre (TMC) these were 1.0 to 3, 2.7 to 30.55 and 1 to 11; in the National Children’s Hospital (NCH) 1 to 3, 7.14 to 27.27 and 1 to 4; in the East Avenue Medical Centre (EAMC) these were 0 to 3; 0 to 13.04 and 0-4; and in
the Rizal Medical Centre (RMC) the averages were 0 to 2, 5.12 to 25 and 2 to 8 respectively, thereby indicating the low receptivity of the five public hospitals to DF/DHF transmission (Table 1). The results revealed that the breeding of Ae. aegypti occurred throughout the six months in the five public hospitals in Metro Manila. The breeding index was very low during the cool months of January and February and the hot months of March and April in all the hospitals surveyed. The proportion of breeding containers of Ae. aegypti as presented in Table 2 showed that fresh water plant vases were the major indoor containers inspected in the five public hospitals. The results revealed that Ae. aegypti bred in both indoor and outdoor breeding sites. The indoor containers searched and found infested with larvae were fresh water plant vases, drums
Table 1: Monthly Ae. aegypti indices of five public hospitals in Metro Manila during September 2001 to April 2002 San Lazaro Hospital (SLH) Month October November December January February March Indices PI 4.0 2.0 4.0 1.0 2.0 0 ICI 0 31.0 8.3 4.76 4.5.0 0 OCI 36 75 100 33.3 33.3 0 CI 4.0 41.1 15.38 8.3 8.0 0 BI 4 7 4 2 2 0
Tondo Medical Centre (TMC) Month October November December January February March Indices PI 3 2 1 1 1 1 ICI 18.75 28.57 5.55 18.75 11.11 11.11 OCI 40.0 27.77 25.0 40.0 0 0 CI 30.55 28.0 14.70 30.55 2.70 5 BI 11 7 5 11 1 1
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National Children’s Hospital (NCH) Month October November December January February March Indices PI 2 3 1 1 3 1 ICI 21.4 30 9.09 12.5 0.4 9.09 OCI 0 0 8.33 0 0 0 CI 20 27.27 11.11 11.11 36.36 7.14 BI 3 3 1 1 4 1
East Avenue Medical Centre (EAMC) Month November December January February March April Indices PI 1 2 1 3 3 0 ICI 2.4 5.26 1.92 12 14.2 0 OCI 50 33.3 0 0 0 0 CI 8.33 9.52 1.72 10.7 13.04 0 BI 4 4 1 3 3 0
Rizal Medical Centre (RMC) Month September October November December January February Indices PI 1.0 1.0 1.0 2.0 0 0 ICI 1.5 25.0 5.8 11.76 0 27.27 OCI 25.0 53.3 14.28 7.4 22.22 22.22 CI 5.12 17.02 5.88 14.28 15.38 25.0 BI 4 8 2 3 3 2
PI = Premise Index (%), ICI= Indoor Container Index (%), OCI = Outdoor Container Index (%), CI = Container Index (%), BI = Breteau Index (per 100 rooms)
and basins, while the outdoor containers positive for Aedes larvae were fresh water plant vases, empty paint cans, discarded plastic cups, drums, used automobile tyres, empty bottles and abandoned toilet bowls. These receptacles provided breeding in both dry and wet seasons (Table 3).
Ovitrap survey The Ovitrap Index indoors was also observed to build up from October to January (Table 4). The findings were contrary to reports that the breeding was only confined to the wet season. The Mean Ovitrap Index varied from 0.0 to 48.5
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Table 2: Percentage of indoor containers inspected in five public hospitals Type of containers Fresh water plant vase Basin Pails Plastic drums (orocan) Plant saucer Total RMC 59 (40.69%) 1 (0.69%) 43 (29.65%) 42 (28.97%) 0 145 (100%) TMC 59 (76.62%) 0 13 (16.88%) 3 (3.90%) 0 77 (100%) NCH 41 (64.06%) 0 9 (14.06%) 14 (21.88%) 0 64 (100%) EAMC 90 (46.40%) 0 98 (50.51%) 6 (3.09%) 0 194 (100%) SLH 166 (80.60%) 0 9 (4.36%) 29 (14.07%) 2 (0.97%) 206 (100%)
Table 3: Number of indoor and outdoor containers positive for Ae. aegypti in five hospitals in Metro Manila, during September 2001 to April 2002 Type of containers Freshwater plant vase Drums Basins Empty coconut shells Plastic cups Tin cans Used tyres Empty paint cans Abandoned toilet bowls Decorative jars Figures in brackets indicate percentage
Indoors No. searched 356 1 1 0 0 0 0 0 0 0 Positive 50 (14) 1 (100) 1 (100) 0 0 0 0 0 0 0 11 0 0 1 20 14 38 15 32 2
Outdoors No. searched Positive 4 (360) 0 0 1 (100) 16 (80) 6 (42.8) 4 (10.5) 12 (80) 10 (31.5) 1 (50)
and showed the presence of Ae. aegypti vector in the five public hospitals. The Mean Ovitrap Density Index ranged from 24.98 to 32.58 per positive ovitrap (Table 5). There were 8464 eggs counted and 10% were reared to Aedes larvae, 90% were Ae. aegypti and 10% were Ae. albopictus. This showed that Ae. aegypti bred in the hospitals predominantly over Ae. albopictus. Our study showed that the ovitrap technique could be a reliable tool in vector
surveillance. The ovitrap detected density of Aedes mosquito in hospitals even during hot months.
Conclusion Our study established the high receptivity of five hospitals in Metro Manila (breeding potential) for dengue vectors. The presence
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Table 4: Ovitrap Index San Lazaro Hospital (SLH) Month October November December January February March Indices Oli 23.3 3.3 6.6 20 37 0 OIo 23.3 10 16.6 7 17 0 OIm 23.3 6.6 11.6 13.5 27 0
East Avenue Medical Centre (EAMC) Month November December January February March April Indices Oli 26.6 16.6 6.7 17 13.3 0 OIo 70 10 6.7 37 53 13 OIm 48.5 13.5 7 27 3.3 6.5
Tondo Medical Centre (TMC) Month October November December January February March Indices Oli 3.3 10 13.3 20 3.4 0 OIo 10 23.3 40 57 3.4 3.3 OIm 6.7 17 27 39 3.4 2
Rizal Medical Centre (RMC) Month September October November December January February Indices Oli 17 37 7 20 17 3.3 OIo 10 27 7 20 23.3 3.3 OIm 13.5 32 7 20 40.3 3.3
Oli = Ovitrap Index indoor (%), OIo = Ovitrap Index outdoor (%), Olm = Mean Ovitrap Index
National Children's Hospital (NCH) Month October November December January February March Indices Oli 27 3.33 3.33 7 10 13.3 OIo 7 6.66 6.7 10 17 6.6 OIm 17 5 5 8.5 13.5 10
Table 5: Ovitrap Density Index Name of hospital EAMC SLH RMC NCH TMC 176
No. of eggs (indoor) 898 891 613 296 523
No. of eggs (outdoor) 1741 690 811 792 1209
Total
No. of (+) ovitrap 81 49 57 35 56
Ovitrap Density Index 32.58 32.26 24.98 31.08 30.92
2639 1581 1424 1088 1732
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of key breeding receptacles indoors and outdoors confirmed the presence of dengue vectors, Ae. aegypti and Ae. albopictus, in all public hospitals surveyed. Hospitals are a priority area for surveillance and control of DF/ DHF as they are highly vulnerable, i.e. source of virus through patients. As a result of the study, guidelines for vector control in hospitals were prepared to prevent mosquito breeding in all potential breeding sites of dengue vectors in hospital premises.
Acknowledgements The authors extend their gratitude to Dr Kevin Palmer, Regional Adviser of Malaria and Vector-
borne Diseases, WHO/WPRO Manila, Dr Remigio Olveda, Director (RITM), Dr Rose Z. Capeding, Dr Ma. Nerissa N. Dominguez, Mrs Norma Joson, Research Institute for Tropical Medicine (RITM) Department of Medical Entomology staff, hospital staff and chiefs of Rizal Medical Centre, San Lazaro Hospital, Tondo Medical Centre, National Children's Hospital and East Avenue Medical Centre for their invaluable help in this study. Thanks are also due to Krisstoffere Joy I. Cruz, Darwin Charles I. Cruz, Katherine Rose Ann I. Cruz , Ma. France Kristine I. Cruz and Edward Brian Pineda, for their invaluable support to this study.
References [1] Halstead SB. Epidemiology of dengue and dengue haemorrhagic fever. In: Gubler DJ and Kuno G, eds. Dengue and dengue haemorrhagic fever. New York: CAB International, 1997. pp. 23-44. [2] Department of Health - National Epidemiology Centre (DOH-NEC), Manila. Unpublished report, 1998. [3] Shultz GW. Seasonal abundance of dengue vectors in Manila, Republic of the Philippines. Southeast Asian Journal of Tropical Medicine and Public Health. 1993 Jun; 24(2): 369-75. [4] World Health Organization, Regional Office for South-East Asia. Prevention and control of dengue/dengue haemorrhagic fever: comprehensive guidelines. New Delhi : WHOSEARO, 1999. [5] Lee HL. Sequential sampling: its application in ovitrap surveillance of Aedes (Diptera: Culicidae) in Selangor, Malaysia. Tropical Biomedicine. 1992; (9): 29-34.
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