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Exam II BIO 235 Answers

Exam II BIO 235 Answers

  1. A 37-week-old infant was delivered by cesarean section and discharged from a Connecticut hospital when he was 10 days old. Two days later he was lethargic and had a fever. When he was readmitted to the hospital, he had multiple brain abscesses caused by Citrobacterdiversus. After a prolonged illness, the baby died. A second infant with a normal pregnancy and delivery died of C. diversus meningitis after a short illness. Nine infants in the hospital nursery had umbilical cord colonization by C. diversus. Environmental cultures were negative for hospital equipment.
  2. What is the normal habitat of this gram-negative, facultatively anaerobic, non-endospore-forming, lactose-positive rod?

The normal habitat for C. diversus is water, sewages and feces from both animals and humans where they originate from the intestinal tract, food and soils (Shan-Chwen, 2011).

b.Provide a plan for identifying the source of infection and preventing further infection. (30 points)

Provided that the environmental cultures were negative for hospital equipment, this showed there was another potential source of infection within the hospital. With the death of infants and no traces on hospital equipment, the source of the Citrobactor outbreak may either be through mothers infecting their infants or direct contact with the hospital staffs also considering that it is an opportunistic nosocomial pathogen.

In this case all the hospital staff members should be administered to a laboratory test. In humans it is always located in the intestinal tract; the feces of each staff should be isolated and cultured for the type of bacteria.  It is noted that someone with Citrobactor infection can only be recognized only be a culture and it makes much easier since the citrobactor bacteria spp can grow in different culture medium. Through the test probably a carrier of the bacteria strain will be identified and may be the reason behind the transmission of the infection. After the identification of the carrier or source of infection through a lab test, various precaution and measure should be put in place. The individual should be given the appropriate drug. The hospital staffs should wear the appropriate hospital clothing including gloves to avoid direct contact transmission.






Figure 14.4


2) Salmonella heidelberg gastroenteritis occurred on three cruises aboard the T.S.S. Festivale. Figure 14.4 shows on-board clinic visits for diarrheal illness between February 10 and March 3.

  1. Explain the incidence pattern shown on the graph

Consumption of any substances with droplets of Salmonella   is one way someone can get the bacteria, it spreads first once the food or drinks are in contact with the pathogen (CDC, 2013). From the graph, different periods are show the pathogen was able to spread in the population within a period of less than 20 days.

The numbers of new cases have changed over the period with each group having different rate of infection daily. On tenth, there was a clinical, visit from one of the crew members, again on 13th and 14th there was a recorded cases of clinical visit among 2-3 crew members. From there on no new case were reported until 21st but this time it was passenger .From the graph it shows that the pathogen may have been transferred to the passenger around 13th before the crew made their last clinical visit and got cleared of the infection. In between the days pathogen was multiplying and spreading   among the passengers

On 22nd the number of those infected had increased and continued to increase on 23rd to over 20 passengers. At this time also some of the crew members had become infected and made clinical visit. The rate of clinical visits   fluctuated in crew members as they got infected at different time. Passengers were severely affected as their number of clinical visits increased on 28th; the pathogen had spread widely among the passengers than the crew. The highest clinical visits were on 27th, 28th and 1st, by 3rd March, there were no clinical visits as all cases had been handled.


  1. What are probable modes of transmission?

The possible mode of transmission is consumption of the contaminated food and drinks

  1. What changes would you recommend before the ship books more cruises after March 3? (30 points)

Measures to prevent any outbreak need to be put in place. All the raw food in the ship should be cleaned with clean water. All the perishable food in the ship should be kept away in freezer or somewhere safe. Dairy product have to be pasteurization, all the water on the ship should be treated. The only food allowed for consumption is the one that has been cooked properly. All the utensils should be cleaned before and after use. Any crew member who had been exposed to the pathogen and made clinical visit should not handle any food material for the time being. All the food handlers and other passengers on the ship should always wash their hands after using the wash room, Pets should not be allowed on the ship since they can also transmit the pathogen to the handler who will in turn spread it (Public Health Agency of Canada, 2011).

  1. A 56-year-old Army officer received a smallpox vaccination at a military vaccination clinic. Within 2 weeks, a painful ulcer was noted at the vaccination site. Because of the appearance of an increasing number of peripheral lesions and because of continued enlargement of the initial ulcer, he was treated. Eventual recovery was complicated by Pseudomonas sepsis and the need for a skin graft at the vaccination site. What was the cause of the ulcer and lesions, and what were the treatments? What caused the Pseudomonas infection? (30 points)

The formation of a painful ulcer after the army officer was received small pox vaccine can be explained in different ways, It is either his body immune system was responding to the vaccine introduction into the body. The other possibility is that the equipment used for vaccination was contaminated with a pathogen; the formation of the ulcer was a result of the body responding to the infection.

Pseudomonas spp is a gram negative bacteria, it produces a lot of toxin when on entering the body and spreads very quickly. It is also an opportunistic pathogen. There is chance that the army officer may have got the bacteria from the contaminated equipment used. Also he may have go it somewhere else, whereby it entered the body  through the wound caused by immune response at the site of injection, the most probable source may be warm tap water which is one of the  reservoirs for the pathogen. The presence of pseudomonas spp causes the development of peripheral lesions and increases as the number of bacteria also increase. Treatment using antibiotic like penicillin will be able to kill the pathogen (Flannigan, 2013).



  1. In the West Branch Study what are your thoughts on how the investigation was done? It is a classic study. (10 Points)

The investigation of an outbreak of hepatitis needed to be done quickly to prevent further spread to other areas and also identify the root cause. It was a very challenging task to the CDC (Center of Disease Control) to pin down on the source of the outbreak. It was the second time CDC was using case control method in their study, the method is always retrospective. The methodology required to pick out the correct group of controls and used to trace back the source (CDC, 2013).



Shan-Chwen, C. (2011). Citrobacter species. Antimicrobial TherapyJournal . Retrieved from

Public Health Agency of Canada. (2011). Pseudomonas spp. Pathogen safety data sheet – infectious substances. Retrieved from

Flannigan, L. (2013). Pseudomonas aeruginosa infection.University of Oklahoma. Retrieved from

Center of Disease Control and Prevention. (2013). Salmonella. Retrieved from


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