Gert van der Hoek
In Memoriam - Editor, Senior Moderator
[FONT=Conv_MinionPro-Regular]Outbreak identification and investigation[/FONT]
On 6 and 7 September 2017, the National reference Laboratory for arboviral infections based at the National Institute of Health, Italy, received serum and urine samples from three patients with a history of high fever (>38?C), severe joint pain and an itching skin rash. Symptoms had started while they were on holiday near the coastal town of Anzio, in the province of Rome, Lazio region (ca 58 km from Rome). The dates of symptom onset were 5 and 11 August and 2 September respectively. The patients lived in the same home, and none had travelled to chikungunya, dengue or Zika endemic areas in the two weeks before symptom onset. The two patients who developed symptoms at the beginning of August were chikungunya IgM positive and the infection was confirmed through a neutralisation test (PRNT). The third patient, who was symptomatic at the time of sample collection, was IgM positive and PRNT borderline (PRNT50 ≥ 1:10). Chikungunya virus was detected by RT-PCR followed by nested PCR in both serum and urine and was isolated from urine.
The regional health authorities immediately implemented measures around this initial cluster, which are described in the national plan for chikungunya surveillance and control [1]. The three patients had referred to other individuals in their neighbourhood who had developed similar symptoms since the beginning of August. Epidemiological surveillance was enhanced to identify additional cases (case finding trough general practitioners (GPs), paediatricians, emergency rooms and hospitals). As of 20 September 2017, 86 confirmed autochthonous cases of chikungunya were reported to the regional surveillance system; the investigation is ongoing. These were found among people living in Anzio, or people who had travelled there 15 days before symptom onset. Cases from Rome were also identified, with either travel history to Anzio or to other endemic areas [2]. The primary viraemic case who imported the virus into the region has not been identified so far.
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[FONT=Conv_MinionPro-Regular]Discussion[/FONT]
The outbreak described here is the second autochthonous chikungunya outbreak detected in Italy. The first outbreak, with more than 200 reported cases, occurred between July and September 2007 in the north east of the country, near the Adriatic coast, in the province of Ravenna [9]. Subsequent to it, Italy set up a national plan for the surveillance and control of the disease [1]. The aim of this surveillance system is to monitor imported cases and local transmission, identify outbreaks in a timely fashion, and to prevent transmission from substances of human origin (SoHO). The surveillance is enhanced during the high vector activity season (1 June–31 October). The competent vector, Ae. albopictus, which was first detected in north-western Italy in 1990 [9], is now widely established throughout the country, including the Lazio region. Overall between 2014 and 2016, a total of 128 possible/probable/confirmed imported cases of chikungunya have been notified to the Italian health authorities (mean: 43 cases/year; range: 25 cases in 2015 and 70 cases in 2014). Most cases had a travel history to Central and South America [1].
Anzio, one of the locations where autochonous chikungunya cases were currently detected, is a holiday resort less than one hour drive away from Rome. Many families visit the area until the beginning of the school year, which in 2017 was on 14 September. During the summer, the population density increases in the area owing to the easy commute from Rome. Viraemic individuals exposed in August 2017 are likely to have travelled around resulting in new introductions in receptive areas and challenging the implementation of control measures. The delayed identification of the autochthonous cases in Anzio, a coastal recreational area close to the capital towards the end of summer may have triggered the local transmission in Rome. This suggests an extension of the outbreak and the presence of secondary multifocal transmission chains [10].
The lack of access to closed summer houses after mid-September may hamper vector control activities. Summer 2017 has been characterised by particularly high temperatures and by an unusual dry period from May to August, factors that would normally prevent high mosquito density. However, other concomitant factors favoured the activity and abundance of the tiger mosquito including the presence of numerous peridomestic ‘man-made’ breeding sites within constantly irrigated private gardens.
The identification of the viral strain involved in the current Italian outbreak as one very close to the ECSA strain involved in the ongoing epidemic in Pakistan is not surprising, even if this virus it is not carrying the A226V mutation, which has been involved in the increased susceptibility of Ae. albopictus for infection and transmission of chikungunya virus. Other yet undefined mutations might be responsible for the vector competence of Ae. albopictus, allowing it to sustain the present outbreak. The fact that we found chikungunya RNA in a small size mosquito pool, suggests a high level of virus circulation in the area. The investigation is still ongoing and, due to enhanced surveillance and testing, further cases have been identified, with as of 22 September, 102 laboratory-confirmed cases.
LINK TO FULL REPORT
On 6 and 7 September 2017, the National reference Laboratory for arboviral infections based at the National Institute of Health, Italy, received serum and urine samples from three patients with a history of high fever (>38?C), severe joint pain and an itching skin rash. Symptoms had started while they were on holiday near the coastal town of Anzio, in the province of Rome, Lazio region (ca 58 km from Rome). The dates of symptom onset were 5 and 11 August and 2 September respectively. The patients lived in the same home, and none had travelled to chikungunya, dengue or Zika endemic areas in the two weeks before symptom onset. The two patients who developed symptoms at the beginning of August were chikungunya IgM positive and the infection was confirmed through a neutralisation test (PRNT). The third patient, who was symptomatic at the time of sample collection, was IgM positive and PRNT borderline (PRNT50 ≥ 1:10). Chikungunya virus was detected by RT-PCR followed by nested PCR in both serum and urine and was isolated from urine.
The regional health authorities immediately implemented measures around this initial cluster, which are described in the national plan for chikungunya surveillance and control [1]. The three patients had referred to other individuals in their neighbourhood who had developed similar symptoms since the beginning of August. Epidemiological surveillance was enhanced to identify additional cases (case finding trough general practitioners (GPs), paediatricians, emergency rooms and hospitals). As of 20 September 2017, 86 confirmed autochthonous cases of chikungunya were reported to the regional surveillance system; the investigation is ongoing. These were found among people living in Anzio, or people who had travelled there 15 days before symptom onset. Cases from Rome were also identified, with either travel history to Anzio or to other endemic areas [2]. The primary viraemic case who imported the virus into the region has not been identified so far.
- snip -
[FONT=Conv_MinionPro-Regular]Discussion[/FONT]
The outbreak described here is the second autochthonous chikungunya outbreak detected in Italy. The first outbreak, with more than 200 reported cases, occurred between July and September 2007 in the north east of the country, near the Adriatic coast, in the province of Ravenna [9]. Subsequent to it, Italy set up a national plan for the surveillance and control of the disease [1]. The aim of this surveillance system is to monitor imported cases and local transmission, identify outbreaks in a timely fashion, and to prevent transmission from substances of human origin (SoHO). The surveillance is enhanced during the high vector activity season (1 June–31 October). The competent vector, Ae. albopictus, which was first detected in north-western Italy in 1990 [9], is now widely established throughout the country, including the Lazio region. Overall between 2014 and 2016, a total of 128 possible/probable/confirmed imported cases of chikungunya have been notified to the Italian health authorities (mean: 43 cases/year; range: 25 cases in 2015 and 70 cases in 2014). Most cases had a travel history to Central and South America [1].
Anzio, one of the locations where autochonous chikungunya cases were currently detected, is a holiday resort less than one hour drive away from Rome. Many families visit the area until the beginning of the school year, which in 2017 was on 14 September. During the summer, the population density increases in the area owing to the easy commute from Rome. Viraemic individuals exposed in August 2017 are likely to have travelled around resulting in new introductions in receptive areas and challenging the implementation of control measures. The delayed identification of the autochthonous cases in Anzio, a coastal recreational area close to the capital towards the end of summer may have triggered the local transmission in Rome. This suggests an extension of the outbreak and the presence of secondary multifocal transmission chains [10].
The lack of access to closed summer houses after mid-September may hamper vector control activities. Summer 2017 has been characterised by particularly high temperatures and by an unusual dry period from May to August, factors that would normally prevent high mosquito density. However, other concomitant factors favoured the activity and abundance of the tiger mosquito including the presence of numerous peridomestic ‘man-made’ breeding sites within constantly irrigated private gardens.
The identification of the viral strain involved in the current Italian outbreak as one very close to the ECSA strain involved in the ongoing epidemic in Pakistan is not surprising, even if this virus it is not carrying the A226V mutation, which has been involved in the increased susceptibility of Ae. albopictus for infection and transmission of chikungunya virus. Other yet undefined mutations might be responsible for the vector competence of Ae. albopictus, allowing it to sustain the present outbreak. The fact that we found chikungunya RNA in a small size mosquito pool, suggests a high level of virus circulation in the area. The investigation is still ongoing and, due to enhanced surveillance and testing, further cases have been identified, with as of 22 September, 102 laboratory-confirmed cases.
LINK TO FULL REPORT